BAGHDAD: A Shi'ite Muslim militia in Iraq claimed responsibility on Friday for a deadly rocket attack on an exiled Iranian opposition group housed near Baghdad according to Iran's Fars news agency.

At least 15 rockets crashed in and around the camp of the People's Mujahideen Organisation of Iran (PMOI) next to Baghdad International Airport on Thursday killing 23 members a Paris-based spokesman said.

"We warned the members of this terrorist organisation to leave Iraq as soon as possible ... If they don't do so there will be more similar attacks" al-Mukhtar Army commander Wathiq al-Battat was quoted as saying by Fars.

Reuters could not independently verify the claim. Al-Mukhtar Army has said it receives funding from Tehran. Fars news agency is close to Iran's powerful Islamic Revolutionary Guards Corps.

Shahin Gobadi the PMOI spokesman accused "agents of the clerical (Iranian) regime inside the government of Iraq" of launching the attack and also placed responsibility on the Iraqi government and the United Nations.

An Iraqi government spokesman was not immediately available for comment.

Iranian-backed Shi'ite paramilitary groups seen as a critical deterrent against Islamic State militants controlling about a third of Iraqi territory hold wide sway in Iraq a major OPEC producer.

The United States urged Baghdad to increase security at so-called Camp Liberty and to hold accountable those responsible for the attack. The United Nations also condemned the 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 António Guterres said.

Rights group Amnesty International urged an investigation.

LABELLED "TERRORISTS" THEN "REFUGEES"

Videos posted online by PMOI's political umbrella appeared to show Thursday's attack and aftermath. In one clip the whizzing of rockets can be heard followed by images of explosions and burning buildings.

Footage posted on Friday showed burnt out and collapsed trailers with debris scattered across the muddy ground.

Until a few years ago PMOI also known by its Farsi name Mujahideen-e-Khalq Organisation (MKO) was listed as a terrorist organisation by the United States and the European Union.

The group sided with Saddam Hussein during Iraq's war with Iran in the 1980s but fell out of favour with Baghdad after he was toppled by a U.S.-led invasion in 2003.

PMOI once had a presence in the United States and maintains offices in Europe. Critics have described it as a cult.

The remaining Iranian dissidents in Iraq who seek the overthrow of Iran's clerical leadership established by the 1979 Islamic revolution were disarmed after Saddam's fall and later moved to Camp Liberty.

There have been several attacks against PMOI over the past decade. An estimated 3000 residents at Camp Liberty have been awaiting resettlement abroad for years.

U.S. Secretary of State John Kerry said on Thursday Washington was committed to assisting U.N. refugee agency UNHCR in relocating all of the camp's residents "to a permanent and safe location outside of Iraq."

Reuters