Faleh al-Fayyadh said investigators had yet to determine who was behind the past month's blasts at four training camps and arms depots used by the Hashed, which is mainly composed of pro-Iranian militias.

Fayyadh, who also serves as the government's national security adviser, issued the statement after an emergency meeting with Prime Minister Adel Abdel Mahdi late on Wednesday.

"Preliminary investigations" found the incidents were "an external, premeditated act," he said.

"The investigations will continue until the responsible entities are accurately identified to be able to take the appropriate stances."

Just hours earlier, the Hashed's deputy commander Abu Mehdi al-Muhandis, whose virulent anti-Americanism as a militia leader earned him a US terror blacklisting, had been unequivocal in blaming Washington.

"We announce that the first and last entity responsible for what happened are American forces, and we will hold them responsible for whatever happens from today onwards," Muhandis said.

He said the attacks were carried out by "agents or in special operations with modern airplanes," without providing further details.

Fayyadh said his deputy's statement "does not represent the Hashed's official position".

Meanwhile on Thursday, the Hashed said it targeted an unidentified drone spying on one of its bases on the outskirts of Baghdad.

"The Hashed al-Shaabi targeted a surveillance drone flying over the Brigade 12 base in the Baghdad belt, forcing it to withdraw without finishing its surveillance mission," the group said in an online statement.

Nasr al-Shummary, military advisor to the Hashed, told AFP the drone was unidentified and that it did not crash.

Also on Thursday, Kataib Hezbollah, a member of the Hashed, issued a "final warning" to the United States.

"We issue a final warning to the American enemy that any new targeting of any Iraqi positions will be met with a tough, categorical response," the group said in a statement.

The Hashed, which, with Iranian training and advice, played a key role in the fight against the Islamic State group independently of the US-led coalition, is made up of disparate armed groups that also include some Sunni tribal units.

Analysts say the divergent statements from its top commanders could reflect a wider rift within the alliance.

The Pentagon on Wednesday denied any involvement in the explosions.