WASHINGTON - President Barack Obama said on Tuesday that his administration would reengage Congress on closing the notorious US military run prison at Guantanamo Bay.

"It needs to be closed," Obama said at a White House news conference. "I'm going to go back at this."

Obama's comments came amid reports that as many as 100 prisoners at Guantanamo are on a hunger strike. Obama had vowed in his 2008 campaign to close Guantanamo, but failed to get it done in his first term.

"It' is not a surprise to me that we are having problems at Guantanamo." Obama called Guantanamo unsafe, expensive, and said it lessens cooperation with US allies.

He noted that Congress has legislatively blocked him from closing Guantanamo, but offered no solution to getting around that hurdle.

"I am going to go back at this," said Obama, "I am going to reengage with Congress that this is not in the best interest of the American people."

Obama said Guantanamo might have been seen as necessary after the Sept 11 attacks, but the president says the time to close the prison for high-value terror suspects who were captured on foreign soil is now. "This is a lingering problem that is not going to get better. It's going to get worse," Obama says.

Obama also appeared to defend the Defence Department's decision to force feed the striking prisoners."I don't want these individuals to die," he said.

Meanwhile, Obama addressed intelligence reports that show chemical weapons were likely deployed in Syria. He said it would be a "game-changer" if it is confirmed that Syria used chemical weapons on his people. But when pressed on if confirmation would mean military action, the president only said that it means that his administration would have to rethink its options.

"We don't know how they were used, when they were used or who used them," Obama said.

President Obama had previously drawn a "red line" on the use or transfer of chemical weapons by Assad's regime.

President Barack Obama says the US doesn't know how or when chemical weapons were used in Syria or who used them.

(April 30) Obama said that taking additional action without hard evidence could compromise the US position internationally.

"If we end up rushing to judgment without hard, effective evidence, then we can find ourselves where we can't mobilize the international community to support what we do," Obama said.

But Obama stressed that if it is confirmed that the Assad regime has used chemical weapons, his administration would take new action.

Obama also pushed back against criticism from some Republican lawmakers that have suggested that the FBI dropped the probe when the Russian government asked it to investigate one of the Boston bombing suspects, Tamerlan Tsarnaev, in 2011.

"Based on what I've seen so far, the F.B.I. performed its duties, the Department of Homeland Security did what it was supposed to be doing," Obama said. "But this is hard stuff. I told him that I could not be prouder of him.”