A Saudi man who was detained at the U.S. detention centre at Guantanamo Bay, Cuba, for six years has now become the second-in-command for al-Qaeda's branch in Yemen, according to an online statement allegedly by the group.

The statement, which appeared on a website commonly used by militants purportedly from al-Qaeda, says Said al-Shihri has joined the branch known as "al-Qaeda in the Arabian Peninsula" and is now the group's No. 2.

Al-Shihri, 35, ended up in U.S. custody after he was hospitalized for more than a month for injuries suffered during an air strike in December 2001. He was one of the first detainees sent to the controversial detention centre set up by the George W. Bush administration in response to the Sept. 11 attacks.

The detainee was released from the detention centre in November 2007 and transferred to Saudi Arabia, according to U.S. Department of Defence documents. After that, he apparently travelled to Yemen.

"He managed to leave the land of the two shrines (Saudi Arabia) and join his brothers in al-Qaeda," the statement said.

The Associated Press said Saudi authorities didn't immediately comment on the website statement.

An unnamed Yemeni counterterrorism official was cited by the Associated Press as saying Saudi Arabia had asked Yemen to return a number of wanted Saudi suspects who fled the kingdom last year for Yemen. A man with the same name was among those wanted, the official said.

Guantanamo military tribunal documents allege al-Shihri was an al-Qaeda travel facilitator and trained in urban warfare at Libyan Camp, located north of Afghanistan's capital of Kabul.

He allegedly guided extremists on how to enter Afghanistan and provided money to other fighters, the documents say. In the past, Al-Shihri has denied any links to terrorism.

With files from the Associated Press