United States Defence Secretary Robert Gates says the question of how to close the Guantanamo Bay prison camp while also protecting the safety of the American people is a challenge that his country will continue to face.

Gates says he believes there are ways of dealing with that challenge, but there is also a lot of work to do in the meantime.

He spoke after President Obama signed an executive order to close the detention centre within a year.

An estimated 245 men are still being held there, most of whom have been detained for years without being charged with a crime.

The Pentagon recently reported that 61 former prisoners at Guantanamo have returned to the fight against the US and its allies.