Closing Guantanamo is emerging as a never-ending nightmare for President Barack Obama after he bowed to pressure and backed down from plans to try the accused 9/11 plotters in the heart of New York City.

One year after his landmark promise to shutter the controversial prison at the US naval base in Cuba, Obama has not only missed his self-imposed deadline, but his hands are ever-more tied by the political, legal and humanitarian headache he inherited from his predecessor, George W. Bush.

His special envoy to close the site, Dan Fried, has traveled around the world and found only a small handful of countries willing to take in detainees. "Everything about Guantanamo is hard," he acknowledged Wednesday.

Fried predicted the site would close during Obama's first term, which ends in January 2013 -- a far less ambitious deadline than the president's vow to shutter the prison by January 22, 2010.

More than half of the 192 inmates still at Guantanamo are set to be repatriated or released to third countries.

The site houses a variety of prisoners, ranging from a man arrested by mistake to the self-proclaimed mastermind of the September 11, 2001 attacks.

Ever since the Guantanamo prison opened in 2002, in the heat of the "war on terror," a growing number of obstacles have blocked its path to closure, including a political firestorm over housing the detainees on US soil and the influence of Al-Qaeda in the home countries of detainees that could be released.

"I can't say definitively that Guantanamo is not going to shut but I don't see it happening in the next couple of years," Human Rights Watch counterterrorism adviser Stacy Sullivan told AFP.

John Bellinger, who was an adviser to former secretary of state Condoleeza Rice, predicted Obama would be unable to shutter Guantanamo this year, "and possibly not even" during the next three years.

"Politically, gun-shy Democratic majorities are unlikely to vote to move the Guantanamo detainees into the United States during an election year, and may be unwilling to do so at all," said Bellinger, an expert at the Council on Foreign Relations think-tank.

Democrats are bracing for bruising losses in November's mid-term elections.

Congress passed a bill in June that bars the transfer of any Guantanamo detainee to the United States except for trial.

The Obama administration has announced its intention to purchase a federal prison in Illinois to house around 50 detainees deemed too dangerous to release and who cannot be tried due to tainted or insufficient evidence.

On top of needing a reversal from lawmakers fearful of losing their seats in Congress, the White House will also have to contend with "a lot of opposition to holding people indefinitely in Illinois as opposed to holding them indefinitely in Guantanamo," Sullivan said.

"What's the point? You would just be moving Guantanamo in the US," he said.

Last week, dozens of veterans of the US-led wars in Iraq and Afghanistan wrote to Obama to decry "the hysteria permeating the public debate around these issues."

They pointed to the Obama administration's decision to halt the transfers of any Yemeni detainees to the Arabian Peninsula country, even though they make up around half the prison population at Guantanamo.

The move came after a narrowly avoided Christmas Day attack, when a young Nigerian allegedly trained by an Al-Qaeda branch in Yemen tried to blow himself up aboard a US-bound airliner with nearly 300 people aboard.

"We stand ready to support you as you work to close the Guantanamo prison facility and bring terrorist suspects to justice," the veterans wrote.

"Doing so will make Americans more secure on the battlefield, in the skies and on our own soil."