BAGHDAD - One of five Britons seized by a Shiite extremist group nearly two years ago could be freed "very soon" under a deal to win release of militant leaders held in U.S. custody, an Arabic language Web site reports.

A senior aide to Prime Minister Nouri al-Maliki acknowledged Saturday that contacts were under way to release the five Britons, who were taken hostage in May 2007, but denied a deal had been struck.

The widely read Saudi-owned Elaph Web site quoted a leader of the extremist Asaib Ahl al-Haq, or League of the Righteous, as saying that a video sent this month to the British Embassy in Baghdad showing one of the hostages was part of the deal.

Elaph quoted a leader of the group, identified only by his nickname Abu Ali, as saying the deal was being mediated by an unidentified Iraqi lawmaker.

Abu Ali said that first 10 of the group's members would be released in return for one of the Britons. If that went well, others would be released in stages, the report said.

The first group would include Laith al-Khazali, brother of the league's founder Qais al-Khazali, Elaph said.

The final exchange would free Peter Moore, an information technology consultant, in exchange for Qais al-Khazali and Ali Moussa Daqduq, a Lebanese Hezbollah commander who was captured in Iraq in 2007.

Under a new U.S.-Iraq security agreement, the U.S. military plans to release all detainees this year except those that the Iraqi government wants to prosecute. They will be turned over to the Iraqis.

The British Embassy confirmed receiving a hostage video but refused to say who appeared on it. The BBC said it was Moore, who had appeared in an earlier video shown on Feb. 26, 2008.

Moore and four of his security guards were seized by heavily armed men in police uniforms from the Finance Ministry compound in Baghdad.

The league is a splinter group from the Mahdi Army militia loyal to radical Shiite leader Muqtada al-Sadr.

The U.S. believes the group is backed by Iran, a charge the Iranians deny.

Qais al-Khazali, a Shiite cleric and former aide to al-Sadr, has been in U.S. custody since March 2007. U.S. officials believe al-Khazali's group launched a January 2007 raid on a government compound in Karbala, that killed five U.S. soldiers.