NEW YORK: The National Security Agency secretly tapped into the overseas phone calls of prominent critics of the Vietnam War, including Martin Luther King, Muhammad Ali and two actively serving US senators, newly declassified material has revealed.

The NSA has been forced to disclose previously secret passages in its own official four-volume history of its Cold War snooping activities. The newly-released material reveals the breathtaking — and probably illegal — lengths the agency went to in the late 1960s and 70s, in an attempt to try to hold back the rising tide of anti-Vietnam war sentiment.

That included tapping into the phone calls and cable communications of two serving senators — the Idaho Democrat Frank Church and Howard Baker, a Republican from Tennessee who, puzzlingly, was a firm supporter of the war effort in Vietnam. The NSA also intercepted the foreign communications of prominent journalists such as Tom Wicker of the New York Times and the popular satirical writer for the Washington Post, Art Buchwald.

Alongside King, a second leading civil rights figure, Whitney Young of the National Urban League, was also surreptitiously monitored. The heavyweight boxing champion, Muhammad Ali, was put on the watch list in about 1967 after he spoke out about Vietnam — he was jailed having refused to be drafted into the army, was stripped of his title, and banned from fighting — and is thought to have remained a target of surveillance for the next six years.

The agency went to great lengths to keep its activities, known as operation Minaret, from public view. All reports generated for Minaret were printed on plain paper unadorned with the NSA logo or other identifying markings other than the stamp “For Background Use Only”. They were delivered by hand directly to the White House, often going specifically to successive presidents Lyndon Johnson who set the programme up in 1967 and Richard Nixon.

The lack of judicial oversight of the snooping programme led even the NSA’s own history to conclude that Minaret was “disreputable if not outright illegal”.

The new disclosures were prized from the current NSA following an appeal to the Security Classification Appeals Panel by the National Security Archive, an independent research institute based at the George Washington university. “Clearly the NSA didn’t want to release this material but they were forced to do so by the American equivalent of the supreme court of freedom of information law,” said Matthew Aid, an intelligence historian specialising in the NSA.

Together with William Burr of the National Security Archive, Aid has co-authored an article in Foreign Policy that explores the significance of the new disclosures. In addition to the seven names of spying targets listed in the NSA history, the two authors confirmed the names of other targets on the watch list from a declassified document at the Gerald Ford presidential library in Ann Arbor, Michigan.

They include the actor Jane Fonda, Weather Underground member Kathy Boudin and black power activist Stokely Carmichael. In total, some 1,650 individuals were tracked by the NSA between 1967 and 1973, though the identities of most of those people remain unknown.

Aid told me that, in his view, the new material underscores the dangers of unfettered surveillance. Minaret was initially intended for drug traffickers and terrorist suspects, but was twisted, at the request of the White House, to become a tool for tracking legitimate political activities of war protesters.

“If there’s a lesson to be learned from all this, when we are dealing with a non-transparent society such as the intelligence community that has a vast amount of power, then abuses can and usually do happen.”

Public concern about the clandestine interception of anti-war protesters in Minaret helped prompt debate in Congress that in turn led to the formation in 1978 of the Foreign intelligence surveillance (Fisa) court. Paradoxically, the Fisa court is now at the center of the furore surrounding NSA gathering of phone records and internet data following the disclosures of Edward Snowden.

In a further paradox, the Washington debate leading to the formation of the Fisa court was spearheaded by the Church Committee — a Congressional panel named after its chair, Senator Frank Church. That was the same Frank Church who a few years before had himself been placed on the NSA watch list. “I suspect Senator Church never had any idea the NSA was tapping his phone,” Aid said.

In addition to the new details of Minaret, the declassified passages of the NSA history also disclose the more acceptable face of the agency’s work that played an important part in some of the biggest crises of the Cold War. Its signals tracking of the Soviet Union uncovered evidence in September 1962 that the USSR was put on high alert — a full month before the discovery of nuclear-capable ballistic missiles on Cuban soil provoked the Cuban missile crisis.

A year earlier, the NSA similarly picked up early warning signals that indicated the East German Communist Party was considering blocking all crossing by foot over the border between East and West Berlin — a presage of the building of the Berlin Wall.

By arrangement with the Guardian