William J. Burns, the C.I.A. director, traveled to Kyiv last week for secret consultations with President Volodymyr Zelensky of Ukraine, according to two U.S. officials.

The C.I.A. tries to keep Mr. Burns’s travels secret, and the agency never comments on the topic. But one U.S. official acknowledged Mr. Burns’s visit and said that it was meant to “reinforce our continued support for Ukraine and its defense against Russian aggression.”

Since just before the invasion, Mr. Burns has made periodic visits to Ukraine to meet with intelligence officials and to convey information to Mr. Zelensky. A second American official said that Mr. Burns’ recent visit was an intelligence mission designed “to ensure that information continues to flow both ways.” The visit was earlier reported by The Washington Post.

There was no comment from Mr. Zelensky or his office about the meeting.

The U.S. government has periodically complained that it knows more about Russian military movements and plans than Ukraine’s. Kyiv has often been tight-lipped about its operational plans. But before Ukraine’s September counteroffensive, its officials began to share more about their intentions, allowing the U.S. to provide intelligence that helped Kyiv’s military reshape its plans to target weak points in Russian lines.

Mr. Burns also met with senior Ukrainian intelligence officials on his recent trip, though U.S. officials would not discuss the nature of those discussions.

Mr. Burns, a career diplomat, emerged early in the Biden administration as an emergency envoy and problem solver for the White House. And the intelligence relationship between Washington and Kyiv has been vital to the war effort. Ukraine is heavily dependent on insights from the C.I.A. and other intelligence agencies on Russian planning.

Shortly before the invasion, he traveled to Ukraine to warn Mr. Zelensky and urge him to shore up defenses around Kyiv. The intelligence provided on that trip helped Ukraine fend off the initial attack by elite Russian airborne troops on Hostomel Airport, north of Kyiv.

The latest visit comes at a crucial point in the war. Ukraine is pushing for more heavy Western weapons, the Russian military has changed its general in command, and the war has ground into a stalemate over the winter aside from the fighting in and around Bakhmut.

Other high-level U.S. officials have also visited Ukraine in recent days. On Monday, a delegation including Deputy Secretary of State Wendy Sherman; Jon Finer, the principal deputy national security adviser; and Colin H. Kahl, the under secretary of defense for policy, met with Mr. Zelensky.