A spokesman for the Iraqi Peace Brigades, the fighting force loyal to radical Shiite cleric Muqtada al-Sadr, says dozens of its fighters are traveling to help an offensive to retake Tikrit from the Islamic State group.

Ali al-Mosawi told The Associated Press on Sunday that the men will travel to the Shiite holy city of Samarra, the launching point for operations to recapture Saddam Hussein's hometown. About a dozen heavily armed trucks packed with fighters left Baghdad for Samarra earlier Sunday.

An offensive to liberate Tikrit including the Iraqi military, Shiite militias, police officers and Sunni tribes has been underway since March 2.

Al-Sadr announced last month that he would withdraw the Peace Brigades from fighting following accusations that the militias were responsible for battlefield atrocities.