The commander of Iraq's Shi'ite Muslim al-Mukhtar Army militia claimed responsibility on Friday for a deadly rocket attack on a camp holding members of an exiled Iranian opposition group near Baghdad, according to Iran's Fars news agency. About 15 rockets crashed near the camp of the People's Mujahideen Organisation of Iran (PMOI) next to Baghdad International Airport on Thursday and killed 23 of its members, a Paris-based spokesman for the group said. "We warned the members of this terrorist organization to leave Iraq as soon as possible ... If they don't do so, there will more similar attacks," al-Mukhtar Army commander Wathiq al Battat was quoted as saying by Fars. The Al-Mukhtar Army has said it is supported and funded by Iran's government. The Fars news agency is close to Iran's powerful Islamic Revolutionary Guards Corps. The United States urged the Iraqi government to increase security at so-called Camp Liberty and find those responsible for the attack and hold them accountable. The United Nations refugee agency UNHCR also condemned Thursday's attack. "This is a most deplorable act and I am greatly concerned at the harm ... inflicted on those living at Camp Liberty," U.N. High Commissioner for Refugees Ant?nio Guterres said. The PMOI, also known by its Farsi name Mujahideen-e-Khalq Organisation (MKO), sided with Saddam Hussein during Iraq's war with Iran in the 1980s but fell out of favor with Baghdad after he was toppled by a U.S.-led invasion in 2003. The remaining Iranian dissidents, who seek the overthrow of Iran's clerical leadership established by the 1979 Islamic Revolution, were moved to Camp Liberty in 2012. U.S. Secretary of State John Kerry said on Thursday Washington was committed to assisting the UNHCR in relocating all of the camp's residents "to a permanent and safe location outside of Iraq."