Author Graham Greene's political activities and outspoken criticism of the United States led the FBI to compile reports on him for more than 40 years, according to a British newspaper.

The Guardian says it has obtained documents under the US Freedom of Information Act that show that the US government went to "extraordinary lengths" to track the novelist's activities.

Greene was a spy himself in the 1940s

Greene was one of the most popular British writers of the 20th century and was friends with leaders including Fidel Castro of Cuba and Daniel Ortega of Nicaragua.

One of his most famous books, The Quiet American, has been re-made as a film starring Sir Michael Caine, and re-opened arguments about its views on US foreign policy.

The documents obtained by the Guardian show that US officials monitored him when he talked with Castro until the early hours of the morning, and when he helped his friend, Panamanian socialist general Omar Torrijos, in the 1970s.

Officials also opened and read his mail when he was refused entry into the US during the cold war for being a member of the Communist party, according to the report.

"Unsurprisingly, Greene's views on the United States government policies and actions are not flattering," a cable to Washington said after the novelist gave an interview about Latin America in 1984.

Havana visit

After a 1983 meeting with Castro and Colombian novelist Gabriel Garcia Marquez, US diplomats wrote that the group had "sat up until five o'clock in the morning talking presumably about Our Man in Havana".

Our Man in Havana was one of Greene's most famous books, written in 1958 and set just before the communist revolution in Cuba.

When Greene visited Belize in 1978 as a guest of Torrijos, the US government speculated that "it may be that Greene... had some message" from the general about the dispute between Belize and Guatemala.

Greene, who died in 1991, set many of his works in countries undergoing political and social upheaval, such as The Quiet American, which is about Vietnam at the end of French colonial rule.

He worked in Sierra Leone as an MI6 agent during World War II, under notorious double agent Kim Philby.

In 2000, it was revealed the Vatican put pressure on Greene to change one of his most successful novels, The Power and the Glory, about a whisky-addled priest from Mexico.

Contacts: The Graham Greene Birthplace Trust www.grahamgreenebt.org