The US military has filed murder charges against Omar Khadr, a Canadian who was a teenager when he was captured in Afghanistan and sent to the Guantanamo Bay prison in 2002.

The number of Guantanamo Bay detainees participating in a hunger strike has more than doubled since a month ago to 11, including five who are being force-fed, the US military said.

Dozens of Guantanamo Bay detainees have abandoned a hunger strike, lowering the number of inmates refusing food to 18, the US military says.

A two-storey maximum security jail modelled on a US prison is being built in Cuba, exactly four years after the first terror suspects were placed in makeshift cells in Guantanamo.