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US President Barack Obama has signed a law effectively preventing him from emptying the US detention centre at Guantanamo Bay, Cuba.

In a statement, Mr Obama said he opposed the restrictions but signed them because they were included in a law funding the US military in 2011.

The law forbids him using military funds to transfer Guantanamo inmates to the US, where they could face trial.

Mr Obama pledged in January 2009 to close the facility within a year.

He missed that deadline amid bipartisan opposition to the transfer of Guantanamo prisoners to the US, and their prosecution in civilian courts, and difficulties in finding other countries willing to receive inmates cleared for release.

The new law restricts Mr Obama's ability to transfer Guantanamo inmates to another country by requiring the secretary of defence to certify the destination country has met a series of strict security requirements.

It also forbids the president from using military money to modify or construct detention facilities in the US to house prisoners from Guantanamo.

In a statement accompanying his signing of the bill, Mr Obama condemned the strictures, saying they would hamper his ability to prosecute terror suspects, undermine counter-terrorism efforts and hinder the delicate negotiations involved in transferring detainees out of the prison.

"The prosecution of terrorists in federal court is a powerful tool in our efforts to protect the nation and must be among the options available to us," Mr Obama said.

"Any attempt to deprive the executive branch of that tool undermines our nation's counter-terrorism efforts and has the potential to harm our national security."

Mr Obama pledged to seek repeal of the strictures, but the current Congress is even more opposed to his agenda than the one that passed the bill.

But Mr Obama stopped short of calling the restrictions unconstitutional, as some Democratic-leaning national security experts had urged.

The provisions are set to expire when the US government's fiscal year closes at the end of September.

The law specifically names Khalid Sheikh Mohammed, the self-professed mastermind of the 11 September, 2001 terror attacks.

The Obama administration sought to try Mr Mohammed in federal court in New York City, but withdrew the plan amid fierce opposition from New York officials.

The first Guantanamo Bay detainee tried in federal court, Ahmed Ghailani, was found guilty in November of conspiracy to damage or destroy US property with explosives but acquitted on 284 other charges.

Mr Obama pledged to close the Guantanamo Bay detention centre during the 2008 campaign and one of his first acts in office was to order it to close within a year.