The United States has sent five detainees from the prison at Guantanamo Bay to Kazakhstan, marking a renewed push by President Barack Obama to close the controversial jail.

Two Tunisian and three Yemeni inmates who had spent more than 11 years behind bars without ever being charged in a court arrived in Kazakhstan at 0415 GMT on Wednesday aboard a US military aircraft, the Pentagon said.

The prison was set up to hold alleged terror suspects after the September 11, 2001 attacks, but human rights groups have condemned the jail as a "legal black hole," where inmates languish for years without being tried in court.

The pace of transfers from the US-run detention center at Guantanamo has picked up in recent months as Obama attempts to fulfill his vow to shut the prison, despite opposition from some lawmakers.

US officials said more releases would be announced soon.

"We are determined to responsibly reduce the detainee population and you can expect additional transfers over the coming weeks," an administration official told AFP.

The Pentagon said in a statement that the five men "were unanimously approved for transfer" after a thorough review by a task force of several US government agencies.

Details of what Kazakhstan had agreed to and what security steps the government might undertake related to the former detainees remained unclear.

It was the first time the Central Asian country had taken in former Guantanamo detainees.

The transfer of the five men leaves 127 inmates at the remote prison, which is located at a US naval base in southeast Cuba.

The move came just days after Obama's envoy overseeing the release of Guantanamo inmates, Cliff Sloan, resigned from his post. Sloan had reportedly become frustrated at how long it took the Pentagon to approve transfers of detainees.

- More cleared for transfer -

The detention "facility" is approaching its 13th anniversary, as the first detainees arrived on January 11, 2002.

Of the 127 inmates still held there, 59 are cleared to be transferred to their home countries or third countries.

With the release of the two Tunisian detainees, there is only one Tunisian national still held at the prison. At one point, there were 12 Tunisian inmates at the jail.

Yemeni detainees are the largest group at Guantanamo, with 80 inmates identified as Yemeni nationals, of which 50 are considered ready to be transferred. But US authorities are reluctant to send them back to their home country amid concerns over security given unrest in Yemen.

The Pentagon identified the Tunisian nationals transferred Tuesday as Adel Al-Hakeemy, and Abdullah Bin Ali Al-Lufti, also known as Lofti Bin Ali.

Authorities had approved the repatriation of Ali in 2006.

But a US federal judge in 2007 blocked his transfer, saying he would likely face torture and "irreparable harm" at the hands of Tunisian authorities.

Ali, 49, who has a pacemaker and suffers heart rhythm problems, has strongly denied having any links to Al-Qaeda. He insisted he had traveled to Pakistan to buy medicine when he was arrested by authorities there after the 9/11 attacks.

His compatriot, Hakeemy, also known as Hkiml, 49, had been described by US authorities as a "veteran terrorist" who had allegedly taken part in fighting in Bosnia and was accused of links with an Algerian Islamist group.

But he has maintained he was working as a cook in Italy and had gone to Pakistan to find a wife. He was arrested by Pakistani authorities near the Afghan border and held at Guantanamo for more than 12 years.

Both he and his fellow Tunisian detainee had lived in Italy as immigrants.

The three Yemenis who were transferred were identified as Asim Thabit Abdullah Al-Khalaqi, Muhammad Ali Husayn Khanayna and Sabri Muhammad Ibrahim Al Qurashi.

Khalaqi, 46, born in Saudi Arabia, had been suspected of serving in Osama bin Laden's Arab brigade.

Arrested in December 2001 in the company of a senior Al-Qaeda figure, he has been behind bars at Guantanamo since January 17, 2002, among the first inmates to be sent to the prison.

The second Yemeni to be transferred out is Muhammad Ali Husayn Khanayna, 46, also known as Muhammed Ali Hussein Khnenah, who has been held at the prison since June 2002.

He was arrested at the Pakistan-Afghanistan border in December 2001. US authorities alleged he was present at bin Laden's hideout in the Tora Bora mountains and that he had stayed at guesthouses used by Al-Qaeda extremists.

The third Yemeni detainee transferred was 44-year-old Sabri Muhammad Ibrahim Al Qurashi, who had been suspected of membership in Al-Qaeda and undergoing instruction at one of the group's training camps.

He was arrested by Pakistani authorities at a known Al-Qaeda safe house in February 2002 and was sent to Guantanamo in May of that year.