CNN

By Tim Lister, Ivana Kottasovxc3xa1, Julia Hollingsworth and Laura Smith-Spark, CNN

Ukraine has accused Russia of committing xe2x80x9cwar crimesxe2x80x9d in an attempt to weaken its countryxe2x80x99s resistance, as Ukrainian forces engage in fierce fighting with Russian troops in multiple cities across the country.

In the capital, Kyiv, residents awoke Sunday to find the city still firmly under Ukrainian control, despite two massive explosions some 30 kilometers, or about 18 miles, south of the city lighting up the sky overnight.

Fighting has broken out on the streets of Kharkiv, Ukrainexe2x80x99s second largest city, after Russian forces entered the city, Oleh Synehubov, the head of the Kharkiv Regional State Administration, said Sunday. xe2x80x9cDo not leave your shelters!xe2x80x9d he posted on Facebook, warning civilians not to go out on the streets. Ukrainian forces had managed to deter the Russians for the past three days.

Russiaxe2x80x99s unprovoked assault on Ukraine is now entering its fourth day. But despite being far better equipped, Russia has failed to take control of key cities, as ordinary Ukrainians and reservists join efforts to defend their homes and families.

Ukrainian President Volodymyr Zelensky on Sunday accused Russian troops of targeting civilians, including children, and called for an international investigation into the conflict.

The Russian Ministry of Defense has previously said it is targeting only military infrastructure, saying in a statement: xe2x80x9cThe Armed Forces of the Russian Federation do not strike cities and towns, they take all measures to save the lives of civilians.xe2x80x9d

But Zelensky rejected this, saying: xe2x80x9cThey lied when they said they would not target civilian population. Since the first hours of the invasion, Russian troops have been hitting civilian infrastructure.xe2x80x9d

Ukraine is xe2x80x9cdocumenting their crimes,xe2x80x9d he said, adding: xe2x80x9cThis is terror.xe2x80x9d

In another video message, Zelensky said he would be willing to hold talks with Russia but rejected the Russian proposal for a meeting to be held in Belarus, pointing out that Russian military actions are being launched from the country.

xe2x80x9cOf course we want peace and want to meet. We want to end the war. Warsaw, Bratislava, Istanbul and Baku were offered to Russia. Any other cities are fine with us as long as there are no missiles flying from this country,xe2x80x9d Zelensky said, addressing Belarus directly.

According to the Kremlin, a Russian delegation has arrived in Belarus for notional talks, Russian state news agency RIA-Novosti reported Sunday.

Russian offensive failing, Ukrainian PM says

On Saturday, Ukrainian Prime Minister Denys Shmyhal said Russiaxe2x80x99s offensive was failing and it was now deliberately attacking civilian infrastructure, including kindergartens, residential blocks and xe2x80x9cbuses with childrenxe2x80x9d xe2x80x94 actions he labeled as xe2x80x9cwar crimes.xe2x80x9d

xe2x80x9cFor these crimes, the Russian command will surely see military tribunal,xe2x80x9d Shmyhal said at a press conference Saturday. xe2x80x9cThe enemy will surely be punished for killing Ukrainian children.xe2x80x9d Russia has previously maintained it is not targeting civilian areas.

xe2x80x9cThe Russian government doesnxe2x80x99t understand they are not fighting only with the government, in fact they are fighting against the entire Ukrainian people,xe2x80x9d he added.

Russian troops are facing a determined and highly-motivated Ukrainian resistance, resulting in significantly slower progress than Kremlin military planners had first anticipated, according to an assessment issued by Britainxe2x80x99s Ministry of Defence late Saturday.

xe2x80x9cIntensive exchanges of rocket artillery overnight have been followed by heavy fighting between Russian and Ukrainian forces in Kharkiv,xe2x80x9d another British assessment said Sunday. After encountering strong resistance in Chernihiv, Russian forces were now bypassing the area to prioritize xe2x80x9cthe encirclement and isolation of Kyiv,xe2x80x9d it added.

Russia is facing unexpected difficulties supplying its forces, and is experiencing heavier losses in personnel, armor and aircraft than expected, two senior United States officials with direct knowledge told CNN.

Ukrainian Maj. Gen. Borys Kremenetsky told reporters Saturday that Ukraine had captured around 200 Russian soldiers, some of whom were just 19 years old. They were not trained at all and were badly equipped, he said. CNN has not been able to independently verify this.

Russia has yet to establish air supremacy over Ukraine, one US official said, as the Ukrainian Air Force and air defense systems fight for control of the airspace. Without uncontested control of the skies, it becomes more difficult for an army on the move to see and strike targets from the air.

So far these challenges have prevented the quick overthrow of major Ukrainian cities, including the capital, which US officials were concerned could play out in a matter of days. The city of Kharkiv near Ukrainexe2x80x99s border with Russia also has not fallen to invading forces xe2x80x94 despite officials worrying that could happen on the first night of an invasion.

A NATO official agreed that Russian forces were having problems.

xe2x80x9cThey lack diesel, they are proceeding way too slow and morale is obviously an issue,xe2x80x9d said the official.

Asked whether Russians are likely to intensify their efforts, the official said they have no choice. xe2x80x9cThey are way behind schedule,xe2x80x9d the official said. xe2x80x9cThis is getting out of hand for them, every additional day is very painful.xe2x80x9d

But the Russians on Sunday countered reports of its military stalling, claiming the cities of Kherson and Berdyansk xe2x80x9cwere completely blockedxe2x80x9d by Russian forces, and the city of Henichesk and the Chornobayivka airfield near Kherson, also known as Chernobayevka, had both been brought under control.

Maj. Gen. Igor Konashenkov, the Russian Ministry of Defense spokesperson, said a Ukrainian anti-aircraft missile regiment surrendered in the Kharkiv region and 471 Ukrainian servicemen were captured.

CNN could not immediately verify those claims.

Ukrainian Defense Minister Oleksiy Reznikov said on Sunday that checkpoints would be set up across the country to to detect Russian troops and make their movements more difficult. This, he said, was xe2x80x9ca necessary safety measure that will save many lives.xe2x80x9d

Accusations of war crimes

Concerns are now growing that Russia may look to deploy indiscriminate battlefield weaponry in civilian areas in an attempt to decisively crush Ukrainian forces.

A CNN team spotted a Russian thermobaric multiple rockets launcher south of Belgorod, Russia, near the Ukrainian border early Saturday afternoon.

Thermobaric weapons have been used in Chechnya, with horrifying consequences, according to Human Rights Watch, and their use has been condemned by number of non-governmental organizations.

There is no evidence that thermobaric weapons have been used in the conflict in Ukraine.

Though Russia has claimed it is not targeting civilian infrastructure, an increasing body of evidence on the ground suggests otherwise.

Ukraine has reported multiple civilian deaths, including a 6-year-old boy who died in heavy gunfire in a western district of Kyiv Saturday evening, according to a local hospital.

A woman was killed after a nine-story residential building in the eastern city of Kharkiv was hit by xe2x80x9cenemy artilleryxe2x80x9d on Saturday night, according to Ukrainexe2x80x99s State Emergency Service.

And on Saturday, a large residential apartment block in the west of Kyiv was struck by what a Ukrainian government minister described as a Russian missile, as residents across the city were forced to seek shelter after a terrifying night punctuated by gunfire and explosions.

The UN Office for the Coordination of Humanitarian Affairs said late Saturday that the United Nations xe2x80x9creports at least 240 civilian casualties, including at least 64 people killedxe2x80x9d in the fighting in Ukraine. Damage to civilian infrastructure has deprived hundreds of thousands of people of access to electricity or water, the statement added.

A defiant Ukraine

As the battle continues, a defiant Zelensky has released a series of videos urging citizens to defend their country.

Officials armed reservists with 18,000 guns and ammunition in Kyiv alone, and Ukrainian TV has broadcast instructions for making Molotov cocktails. Ukrainian males ages 18 to 60 are banned from leaving the country.

xe2x80x9cEach Ukrainian should keep one thing in mind: if you can stop and destroy the occupiers xe2x80x94 do it. Everyone who can come back to Ukraine xe2x80x94 come back to defend Ukraine,xe2x80x9d Zelensky said in a video message Saturday.

xe2x80x9cWe have withstood and successfully repelled enemy attacks. Fighting continues in different cities and regions of our country,xe2x80x9d he said, adding that the capital Kyiv and key towns around it were still under Ukrainian control. xe2x80x9cWe have ruined their plans. They have no advantage over us.xe2x80x9d

In a statement Sunday, Zelensky called on citizens of the world to join the fight against the xe2x80x9cRussian war criminals.xe2x80x9d

xe2x80x9cThis is not just Russiaxe2x80x99s invasion of Ukraine. This is the beginning of a war against Europe, against European structures, against democracy, against basic human rights, against a global order of law, rules and peaceful coexistence,xe2x80x9d he said.

At the same time, thousands of Ukrainians are fleeing for their lives. More than 150,000 people have fled Ukraine, most of them to Poland, UN High Commissioner for Refugees Filippo Grandi said Saturday.

The Polish border guard said Saturday that 100,000 people have entered Poland from Ukraine since the invasion began Thursday.

Controlling the narrative in Russia

At home, the Kremlin appears to be in damage control, attempting to limit information about the difficulties its forces are facing in Ukraine.

Social media platform Twitter said Saturday it is being restricted inside Russia and is working to address the issue.

According to the assessment issued by Britainxe2x80x99s Defense Ministry late Saturday, the Russian government has reportedly restricted access to a number of social media platforms in a xe2x80x9cprobable attempt to conceal details regarding the situation in Ukraine from their own people.xe2x80x9d

Russiaxe2x80x99s media regulator told 10 news outlets that it would restrict access to their publications unless they stopped spreading xe2x80x9cfalse informationxe2x80x9d xe2x80x94 including the shelling of Ukrainian cities and the death of civilians caused by the Russian armed forces.

Opposition to the war is also being restricted in the country. More than 2,600 people have been detained in Russia after taking part in anti-war protests, according to independent protest monitoring site OVD-Info. At least 1,370 of them were detained in protests in Moscow, according to the same site.

The-CNN-Wire
xe2x84xa2 & xc2xa9 2022 Cable News Network, Inc., a WarnerMedia Company. All rights reserved.

CNNxe2x80x99s Tim Lister and Ivana Kottasova reported from Kyiv. CNNxe2x80x99s Victoria Butenko, Nathan Hodge, Josh Campbell, Jonny Hallam, Jim Sciutto, Oren Liebermann, Mia Alberti, Olena Mankovska, Anna Chernova, Vasco Cotovio, Frederik Pleitgen, Ruba Alhenawi and Olga Voitovich contributed to this report.