The Yemeni branch of al-Qaeda says its top cleric, Ibrahim al-Rubaish, was killed late on Sunday in a drone strike, alledegly by the Unite States, AQAP said in a statement published Tuesday.Al-Qaida said in a statement posted on Twitter that Ibrahim al-Rubaish was killed, along with other unnamed members of the group, by a drone late on Sunday. The statement did not specify the location of the drone attack.Yemeni and U.S. officials had no immediate comment on the claim.Al-Rubaish, believed to be in his late 30s, was released from Guantanamo Bay in 2006, after which he joined al-Qaida in Yemen. He was considered the group's the main ideologue and theological adviser and his writings and sermons were prominent in its publications.If the drone attack is confirmed, it would be the first use of unmanned aircraft since Yemen sank further into turmoil last month, prompting a Saudi-led coalition to launch airstrikes on March 26 in an attempt to halt Yemen's Shiite rebels known as Houthis who have taken over much of the country.The Houthi advance has also forced Yemen's Western-backed President Abed Rabbo Mansour Hadi to flee the country as his government crumbled.U.S. officials have said the collapse of Hadi's government could undermine Washington's counterterrorism strategy against al-Qaida's branch in Yemen, known as Al-Qaida in the Arabian Peninsula. Washington considers the branch to be the most powerful in the terrorist network.In late March, about 100 U.S. military advisers withdrew from the al-Annad air base where they had been leading the U.S. counterterrorism efforts in Yemen.U.S. officials also said that CIA drone strikes would continue but that there will be fewer of them.