Updated

The U.S. military has released a Shiite militant accused of being involved in the 2007 killing of five American soldiers, officials said Tuesday.

Laith al-Khazali's release comes amid reports of negotiations with his militia group to free at least one of five British hostages.

Al-Khazali and his brother Qais, who were both detained in March 2007, are accused of organizing a bold raid on a local government headquarters in Karbala that killed five U.S. soldiers on Jan. 20, 2007. The brothers are leading members Asaib Ahl al-Haq, or League of the Righteous, which is allegedly backed by Iran.

A British Foreign Office spokesman said the release was part of "the wider Iraqi government reconciliation process of reaching out to groups that are willing to set aside violence in favor of taking part in the political process."

The spokesman declined to be identified in line with department policy.

A follower of anti-U.S. cleric Muqtada al-Sadr also said that al-Khazali has returned home to Baghdad's mainly Shiite district of Sadr City. The Sadrist official spoke Tuesday on condition of anonymity because he's not authorized to comment on the issue.

The U.S. military has been releasing detainees or transferring them to Iraqi custody as part of a security pact that took effect on Jan. 1.

Al-Khazali's release takes on added significance because it follows reports of an agreement that one of five British hostages would be freed in exchange for the release of 10 members of Asaib Ahl al-Haq.

The U.S. military believes the extremist network is one of the main so-called Iranian-backed "special groups" that have refused to adhere to a cease-fire called by al-Sadr. The other is Kataib Hezbollah or Brigades of the Party of God.

Iran's government denies having any links to Shiite extremists in Iraq, but American officials believe the two groups are controlled by the Iranian Revolutionary Guards' elite Quds Brigade, which trains Shiite militants from various Middle Eastern countries.

In March, the widely read Saudi-owned news Web site Elaph quoted an Asaib Ahl al-Haq leader as saying one of the five Britons would be freed "very soon" in exchange for 10 of its members.

If that exchange goes according to plan, the other hostages would be released in stages in exchange for the freedom of more detained Shiites, according to the report. The first group of detainees would include Laith al-Khazali, it said.

The five Britons — a management consultant named Peter Moore and four of his security guards — were seized by heavily armed men in police uniforms in May 2007 from the Finance Ministry. They were driven away toward Baghdad's Shiite enclave of Sadr City.

The British Embassy received a new video showing one of the hostages, who was not identified, in March.

Moore, who worked for BearingPoint, a U.S.-based management consulting firm, also appeared in a video that was aired on the pan-Arab station Al-Arabiya in February.

At that time, he called on British Prime Minister Gordon Brown to accede to the kidnappers' demand for a trade for Iraqi prisoners. "It's as simple as that," he could be heard saying. "It's a simple exchange of people."