Washington (AFP) - The Central Intelligence Agency on Wednesday declassified a trove of secret daily briefings given to presidents Richard Nixon and Gerald Ford, offering fresh insights into pivotal moments in Cold War history.

The 2,500 previously classified daily intelligence briefings are peppered with details about the slowly unfolding catastrophe in Vietnam, various international crises and attempts to understand the machinations of Soviet and Chinese leaders.

The 28,000 pages offer tantalizing new insights into the context of Nixon's historic visits to China and the Soviet Union -- firsts by a sitting US president -- and his eventual disgrace and resignation.

The briefings during the Ford administration detail the fall of Saigon, the evacuation of Lebanon and Mao Zedong's death.

On February 21, 1972, the day that Nixon landed in Beijing, the CIA carefully noted which Chinese officials appeared at which events, trying to glean a better idea of the workings of the politburo -- political theater that is still closely watched today.

Briefers later informed Nixon that the visit unnerved Moscow, worried Tokyo and encouraged European powers to engage with China.

Beijing, on the other hand, was "generally pleased" with the visit.

On August 10, 1974, newly sworn-in president Gerald Ford's briefing deals in detail with the global response to Nixon's shock resignation.

"None of the potential troublemakers has produced even a rumble," his briefers noted.

Most days, the daily ritual would not be so positive.

On the last day of April 1975, Ford was bluntly informed that "President Minh surrendered Saigon unconditionally this morning."

"The flag of the Viet Cong's Provisional Revolutionary Government was hoisted over the presidential palace at 12:15 today Saigon time, marking the end of 30 years of war in Vietnam."

A year and a half later, Ford was informed that Chairman Mao had died.

"Mao had been an important member of the Chinese Communist Party since its founding in 1921," the CIA noted in an initial understatement, before examining the implications of the death of a man who was the "dominating force in Chinese politics."

Senior members of the Communist Party, the CIA speculated, may have been relieved by his death, which ended fears of reprisals.