The final batch of taped conversations secretly recorded by US president Richard Nixon and then used to help bring him down during the Watergate scandal were released on Wednesday.
The latest tapes, recorded between April and July 1973, coincided with a period of rapprochement with the Soviet Union following the US withdrawal from Vietnam and the congressional investigation of Watergate.
The 340 hours of recordings were released in mp3 format on the website of the Richard Nixon Presidential Library in Yorba Linda, Calif.
Most of the conversations related to Watergate have been previously released.
The latest batch includes a poor-quality recording of Nixon meeting with his Soviet counterpart Leonid Brezhnev in the Oval Office during an historic June 1973 summit.
Nixon, who was elected in 1968 and again in 1972, installed an extensive system of recording devices throughout the White House and the presidential retreat at Camp David.
Hundreds of hours of the recordings remain classified for national security reasons.
The existence of the recording system, installed in February 1971, was revealed during the inquiry into Watergate in July 1973, prompting the White House to order its removal.
A year later Nixon, facing possible impeachment over the Watergate scandal, resigned in disgrace.
Tapes archivist Cary McStay said there are currently no plans to transcribe the tapes, but that the library has produced subject logs to help guide researchers.
The Nixon tapes themselves are kept in Washington, DC by the National Archive.