The Russian leader, Boris Yeltsin, gave President Clinton about 80 documents related to the assassination, which happened at the height of the Cold War on 22 November 1963.

Documents are proof of improved US-Russian relations, officials say

Lee Harvey Oswald, the man identified as JFK's killer in the Warren Commission report on the assassination, lived in the Soviet Union between 1959 and 1962.

He married a Russian women, Marina, whom he brought back to the US.

Correspondents say the Russian documents, from presidential and foreign ministry files, could shed light on Oswald's stay.

The documents also include a file on the Soviet government's reaction to President Kennedy's death, the Interfax news agency reported.

The documents were handed over during talks in Cologne between the two presidents, designed to mend relations damaged by Nato's bombardment of Yugoslavia, which was opposed by Russia.

'Interesting gift'

William Joyce tells the BBC what he thinks the documents contain

US National Security Adviser Sandy Berger described the documents as "a very interesting gift" and said they were the result of an extensive search of Russian archives ordered by Mr Yeltsin several years ago.

Mr Berger said the documents would be translated from Russian, analysed and "all interesting elements" would be made public.

William Joyce, a former member of the Assassination Records Review Board, also welcomed the disclosure of the documents.

Kennedy assassination came at the height of Cold War

"It will help to have additional information about the [assassination], its context and its background," he told the BBC.

"One hopes that whatever is released will provide maybe a bit more information - fill in a few more gaps - and help us come to a more confident understanding of what happened."

After the collapse of the Soviet Union in 1991, Russia's intelligence agency declassified its files on Lee Harvey Oswald.

But at the time, Russian intelligence officers said the documents shed no new light on the Kennedy assassination.