By Paul Reynolds
World affairs correspondent, BBC News website
There are still some 200 prisoners in the Guantanamo prison camp
US President Barack Obama's decision to suspend the repatriation of Yemeni prisoners from Guantanamo Bay is another blow to his hopes of closing the camp within the foreseeable future.
The president is finding that the reshaping of his security policy to deal with threats from al-Qaeda is leading to difficult decisions as he seeks to balance his own intentions with the security realities.
He has previously admitted that his initial target - to shut Guantanamo by 22 January, just after a year since he took office - will pass unfulfilled.
The possibility is increasing that, even if Guantanamo itself closes, the system itself will not close. This is because there is a rump of detainees the US will not free or put on trial either in a civilian court or a military tribunal.
This decision has just added to them.
Such detainees, including now the Yemeni ones, might face indefinite detention without trial, if not at Guantanamo, then in a new facility at Thomson in Illinois.
This would require congressional approval. At the moment only prisoners facing prosecution, among them the alleged ringleaders of the 9/11 attacks, can be transferred to the United States mainland.
Congressional agreement would not be impossible but would require long negotiations.
The suspension will affect about 30 Yemeni prisoners, out of the 200 or so detainees who remain in the camp.
GUANTANAMO IN NUMBERS
Detainees since 2002: 779
Detainees transferred: 575
Detainees died in custody: 6
Detainees still in custody: 198
Countries of citizenship: 48
Afghan citizens: 221
Saudi Arabian citizens: 139
Yemeni citizens: 112
Transfer countries: 44
Transfers to Yemen: 21
Source: New York Times
These Yemeni prisoners have been through a review process and have been cleared for release.
But the alleged attempt to blow up a US airliner by a Nigerian who said he was trained and equipped in Yemen has changed the security outlook.
In addition, two Guantanamo Bay prisoners released previously have become leaders of al-Qaeda in Yemen.
The president does not want to take further risks, especially after castigating the US intelligence services for failing to stop the latest suspect.
But he repeated that the camp will close.
"Make no mistake: We will close Guantanamo prison, which has damaged our national security interests and become a tremendous recruiting tool for al Qaeda," he said.
"In fact, that was an explicit rationale for the formation of al-Qaeda in the Arabian Peninsula."
The US human rights group the Center for Constitutional Rights (CCR) has criticised the decision to suspend transfers to Yemen.
It said: "Dozens of men from Yemen who have been cleared for release after extensive scrutiny by the government's Guantanamo Review Task Force are about to be left in limbo once more due to politics, not facts.
"Many are about to begin their ninth year in indefinite detention.
"Halting the repatriation of Yemeni men cleared by the Task Force after months of careful review is unconscionable.
"It will also effectively prevent any meaningful progress towards closing Guantanamo, which President Obama has repeatedly argued will make our nation safer."
Meanwhile a federal appeals court in Washington has made it harder for Guantanamo Bay prisoners to seek their release.
The court upheld the detention of a former cook for the Taliban, Ghaleb Nasser al-Bihani. He says he never fired a shot but the court rejected his appeal and argued that the administration had the powers to detain him.
The ruling is expected to go to further appeal.