The United States has announced it has transferred two Sudanese detainees from Guantanamo Bay prison to their home country in its second similar release this week as President Barack Obama works to close the facility.

Noor Uthman Muhammed, 51, and Ibrahim Othman Ibrahim Idris, 52, were the last Sudanese prisoners at the US naval base in southern Cuba, a US defence official told AFP news agency on Wednesday.

They were both considered by the US military to be members of al-Qaeda and were sent to Guantanamo in 2002.

Idris, seen by the Pentagon as a "veteran" member of the network who swore loyalty to its late leader Osama bin Laden in the 1990s, was among the first detainees to arrive at Guantanamo Bay on January 11, 2002. Muhammed arrived in May of the same year.

In exchange for a guilty plea to terror offenses in February 2011, part of Muhammed's 14-year sentence was suspended and he completed his term on December 3.

Idris, who had been cleared for transfer since 2009 by an interagency task force, was released after an October court order from the US District Court in Washington.

"As directed by the president's January 22, 2009, executive order, the task force conducted a comprehensive review of Idris's case, which examined a number of factors, including security issues, in making that designation," Pentagon spokesman Lieutenant Colonel Todd Breasseale said.

It said the Obama administration informed the Congress of its intent to transfer both men, as required by law.

"The United States coordinated with the government of Sudan regarding appropriate security measures and to ensure that these transfers are consistent with our humane treatment policy," Breasseale said in a statement.

Third release in December

The transfers came as Obama accelerates repatriations to meet his campaign promise of closing the prison opened by his predecessor George W. Bush in the wake of the September 11, 2001 attacks on the US to house suspects captured around the world.

On Monday, the Pentagon announced the transfer of two detainees, Saad Muhammad Husayn Qahtani and Hamood Abdulla Hamood, to Saudi Arabia.

On December 5, two Algerians were repatriated from Guantanamo, despite the prisoners' protests they could face persecution there.

A total of 158 prisoners now remain at Guantanamo.