Russia gave no security guarantees to US President Joe Biden during his unannounced visit to war-torn Ukraine, Russian intelligence agency director Alexander Bortnikov said on Tuesday.

President Biden slipped into Kyiv on Monday for the first time since Russia invaded Ukraine almost a year ago.

"Indeed, the United States notified Russia about Biden's visit to Kiev - via diplomatic channels. But we gave no guarantees of his security," Federal Security Service (FSB) Director Bortnikov said in an interview with the Shot Telegram channel.

Russia was informed about the trip a few hours before President Biden's departure for "deconfliction purposes", a US official said.

Bortnikov said that Russian and US special services continue to cooperate, especially in what concerns the fight against international terrorism.

"This cooperation continues. Naturally, it is not at the level it used to be at so no one benefits from it. All of us are interested in maintaining ties," Bortnikov was quoted as saying by the official Tass news agency.

Biden's highly secretive visit to Ukraine came at a critical moment in the 12-month conflict. In Kyiv, Biden announced a half-billion dollars in new assistance, saying the package would include more military equipment, such as artillery ammunition, more javelins and Howitzers.

"One year later, Kyiv stands. And Ukraine stands. Democracy stands," Biden said as he met Ukranian President Volodymyr Zelenskyy.

The United States and other Western nations have been rushing arms and ammunition to Ukraine in the hopes of changing the trajectory of the war.

Biden's presence in Kyiv was intended to reaffirm America's "unwavering commitment to Ukraine's democracy, sovereignty, and territorial integrity", according to a White House statement.

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