A rocket apparently fired by fighters from ISIS movement has hit a mosque in eastern Afghanistan, killing six worshipers and wounding four others, a local official said Saturday. The attack in Achin, southeast of Jalalabad in Nangarhar province, occurred during evening prayers Friday, district governor Haji Ghalibhe said. It was not clear if it was aimed at the mosque or went astray after being fired at security forces based nearby. ISIS has been building up its presence in Afghanistan while battling both government forces and the extremist Taliban movement. Nangarhar, on the border with Pakistan, has become one of its main strongholds. Hazrat Hussain Mashriqiwal, a spokesman for the Nangarhar police chief, said security forces had detained two suspects, one of whom was a foreigner. ISIS' rise has caused alarm outside Afghanistan, with Russia saying it was concerned about the threat to its central Asian neighbors and U.S. commanders citing the movement as a reason to delay plans to pull out troops next year.