DUBAI, June 6 (Reuters) - A key Sunni Muslim insurgent group in Iraq said on Wednesday its members had carried out the assassination of the local chief of Shi'ite cleric Moqtada al-Sadr's political movement in a town south of Baghdad. Iraqi police announced on Tuesday that gunmen had shot dead Abdul Raheem Nayef in Jbela, 65 km (40 miles) south of Baghdad. "This apostate was one of the biggest and most hateful enemies of the mujahideen and Sunnis. He had openly fought the unarmed and (Sunni) Muslims," Ansar al-Sunna said in a statement posted on the Internet. "The lions of Ansar ... set up an ambush against him and when he showed up with his bodyguards your brothers attacked them with automatic weapons, killing him instantly," it said. Sunni Muslim militants say the Shi'ite-led government oversees death squads that try to kill Sunnis or drive them out of Baghdad, a charge the government denies. But Iraqi officials have said the movement led by Sadr, an influential anti-American cleric, has been infiltrated by "rogue elements" who are trying to sabotage the political process and are running sectarian death squads. Ansar al-Sunna has claimed several abductions and killings since the March 2003 U.S.-led invasion of Iraq.