WASHINGTON: The FBI suspected that US-born Al-Qaeda cleric Anwar al-Awlaqi, killed in a 2011 drone strike in Yemen, could have bought air tickets for three of the 9/11 hijackers before the attacks, activists said.

Judicial Watch, which is based in Washington, cited government documents obtained under a Freedom of Information Act request which it said suggested the flights were taken shortly before the September 11, 2001 terror strikes.

A heavily redacted FBI document dated barely two weeks after the devastating attacks and published on the US watchdog group's website showed Awlaqi's name and a credit card number alongside that of plot ringleader Mohammed Atta.

The details of transactions carried out using the credit card were unclear from the heavily-censored document, but Judicial Watch said they stemmed from searches of airline reservations made by Awlaqi.

Also named were two other hijackers, who like Atta were Saudi nationals.

The flight listed with Atta's details was for travel between the US capital Washington and Las Vegas, Nevada, and Miami, Florida, dated August 13, 2001.

Less than a month later, Atta was on American Airlines Flight 11 which hit One World Trade Center in New York. Other hijacked planes hit Two World Trade Center and the Pentagon in Washington, while another crashed in Pennsylvania.

The other tickets that Judicial Watch said the FBI suspected had been purchased by Awlaqi were for a Southwest Airlines flight on July 10, 2001 between Fort Lauderdale and Orlando, both in Florida, for hijacker S. Suqami.

Satam al-Suqami was also aboard American Airlines Flight 11, according to the FBI.

The third ticket purportedly was for a hijacker named Al-Sheri for a National Airlines flight from San Francisco to Las Vegas and then on to Miami, apparently to be taken on August 1, 2001.

The Al-Sheri brothers were aboard the same flight as Atta and Suqami.

Awlaqi -- a forceful and somewhat charismatic preacher fluent in Arabic and English -- was seen as a particularly effective global recruiter for the Islamist militant network until he was killed in September 2011.

US President Barack Obama said the killing of Awlaqi in a US drone strike was justified as the suspect was actively plotting deadly attacks against Americans as a leader of Al-Qaeda in the Arabian Peninsula.

US officials believe Awlaqi played a significant role in the attempt to bring down a US airliner over Detroit by an assailant with explosives sewn into his underwear on December 25, 2009.

He was also believed to have coordinated the thwarted 2010 plot to blow up cargo aircraft bound for the United States and had called for attacks against US and Arab governments.