Newly declassified documents show that a CIA field operative accidentally fired on friendly pilots during the failed Bay of Pigs invasion of Cuba in 1961.

The documents were released Monday by George Washington University's National Security Archive. According to the papers, the operative fired rifles and machine guns on B-26 aircraft the CIA had supplied to a Cuban exile invasion force. The bombers were flown by exiles and were configured to look like Cuban military planes. The Archive cites the operative as saying some of the bombers were fired on because no one could distinguish them from the Cuban planes.

It is not clear whether anyone was hurt in the friendly fire incident.

The revelation comes about two weeks after the United States made public four volumes covering the CIA's official history of the failed attack on the government of then-Cuban president Fidel Castro. The document release was a response to a lawsuit filed by the Archive. One volume remains classified.

On April 17, 1961, about 1,500 CIA-trained Cuban exiles landed on Cuba's southern coast in hopes of sparking an uprising. Mr. Castro was warned of the impending invasion and had ample time to prepare his forces. Most of the exiles were arrested and spent time in prison on the island.

John F. Kennedy was U.S. president at the time of the disastrous invasion and took responsibility for it. Many Cuban exiles blamed the botched operation on President Kennedy, saying he did not provide enough support.