U.S. President Barack Obama signs an executive order to close the Guantanamo Bay detention centre within a year during a ceremony in the Oval Office at the White House in January. (Saul Loeb/AFP/Getty Images)

U.S. President Barack Obama has acknowledged that he will not be able to meet his pledge to close the controversial detention centre at Guantanamo Bay, Cuba, by January.

Obama also voiced support for the decision to try the self-professed Sept. 11 mastermind in a U.S. civilian court, predicting his conviction and subsequent execution.

Obama made the comments in a series of TV interviews during his trip to Asia.

In an interview in Beijing with Fox News, Obama said he knew closing down the prison at Guantanamo Bay was going to be difficult.

"It's hard not only because of the politics. People I think understandably are fearful after a lot of years where they were told that Guantanamo was critical to keeping terrorists out. So, I understood that that had to be processed, but it's also just technically hard — I just think as usual in Washington things move slower than I anticipated.

"We are on a path and a process where I would anticipate that Guantanamo will be closed next year," he said. "I'm not going to set an exact date because a lot of this is also going to depend upon co-operation from Congress."

One of Obama's first acts as president was to sign an executive order to close the facility within a year, a move he said would restore his country’s "moral high ground."

But his plan ran into roadblocks. His administration found it difficult to find countries willing to take in the more than 200 detainees.

As well, the U.S. Senate in May voted 90-6 against allowing funds requested to shut down the facility or use the funds to transfer prisoners to U.S. soil.

The Bush administration used the facility to hold suspected terrorists following the Sept. 11, 2001, attacks. But critics have expressed outrage over the tough interrogation techniques used on some of the detainees, saying it amounts to torture. Critics have also complained that prisoners are held for years without charges or trials.

In a separate interview, Obama defended the decision to bring Khalid Sheikh Mohammed and four other detainees at Guantanamo Bay to trial in New York.

"I don't think it would be offensive at all when he's convicted and when the death penalty is applied to him," Obama told NBC News.

But he added that, "I'm not going to be in that courtroom. That's the job of the prosecutors, the judge and the jury."

Obama said Americans should have no concern about the capability of civilian courts to try suspected terrorists.

U.S. Attorney General Eric Holder last week announced the decision to bring Mohammed and four others detained at Guantanamo Bay to trial at a lower Manhattan courthouse.

Appearing before the Senate Judiciary Committee on Wednesday, Holder was asked what might happen if the suspects are acquitted.

"Failure is not an option. These are cases that have to be won. I don't expect that we will have a contrary result," Holder said.

Critics of Holder's decision have argued the trial will give Mohammed a world stage to spout hateful rhetoric.

But Holder said such concerns are misplaced, because judges can control unruly defendants and any pronouncements by Mohammed would only make him look worse.

Holder said the public and the nation's intelligence secrets can be protected during a public trial in civilian court.

The committee's top Republican, Jeff Sessions, criticized the decision, saying it treats Mohammed like a common criminal.

"I believe this decision is dangerous, I believe it's misguided, I believe it's unnecessary," Sessions said.

With files from The Associated Press