Iraq's prime minister's office said on Wednesday it had received “an official verbal message” from Iran informing it that a missile attack on US forces stationed on Iraqi soil was imminent.

Iran launched 22 missiles at Iraqi bases housing US and other coalition troops early Wednesday in response to the killing of senior Revolution Guards commander Qasem Soleimani in a US drone strike in Baghdad last week.

In its first statement hours later, premier Adel Abdel Mahdi's office said it had been warned.

“We received an official verbal message from the Islamic Republic of Iran that the Iranian response to the assassination of Qasem Soleimani had begun or would begin shortly, and that the strike would be limited to where the US military was located in Iraq without specifying the locations,” it said.

The prime minister's office said it was simultaneously contacted by the US, as the missiles slammed into the Ain al-Asad base in western Iraq and Harir further north.

“We immediately warned Iraqi military commanders to take the necessary precautions,” it said, adding that no Iraqi forces had been hurt in the attack.

“Iraq rejects any violation of its sovereignty and attacks on its territory,” the premier's office added, without specifically condemning the missile strikes.

Read | US-Iran conflict: Before and after the killing of Gen Soleimani

It said Abdel Mahdi was in talks with domestic and foreign partners to prevent an “open war.”

Secretary of State Mike Pompeo earlier said he had spoken to Masrour Barzani, the prime minister of the autonomous Kurdish region in northern Iraq.

But it remained unclear if there was any contact between Pompeo or any other top US official and Abdel Mahdi.

Iraq's President Barham Saleh condemned Iran's missile strikes on Iraqi bases, saying he feared “dangerous developments” in the region.

“We condemn the Iranian missile bombing that hit military installations on Iraqi territory and renew our rejection of the repeated violation of state sovereignty and the transformation of Iraq into a battlefield for warring sides,” his office said in a statement.

The speaker of the Iraqi parliament, Mohammed al-Halbusi, also condemned the salvo of retaliatory Iranian missile strikes on Iraqi bases as a “violation of Iraqi sovereignty”.

Halbusi, the most senior Sunni Arab in Iraq's confessional power-sharing system, called for urgent measures to stop Iraq being turned into a proxy battlefield for outside powers, including Shia-majority Iran.

“While we condemn the Iranian violation of Iraqi sovereignty at dawn today... we confirm our absolute refusal to the conflicting parties to use the Iraqi arena to settle scores,” he said.

Iraq pro-Iran factions ramp up threats to US

Meanwhile, a top commander in Iraq's Hashed al-Shaabi paramilitary network said it was time for an “Iraqi response” to a US drone strike that killed the network's deputy chief.

“That response will be no less than the size of the Iranian response. That is a promise,” Qais al-Khazali, a hardline Hashed commander, threatened in a tweet.

Hashed deputy chief Abu Mahdi al-Muhandis was also killed in last week's US drone strike that had killed Soleimani.

The Hashed had already vowed it would retaliate but ramped up its threats after Tehran's missile strikes. Harakat al-Nujaba, a hardline faction within the network, thanked Iran for its attack.

“To American soldiers: Do not close your eyes. Revenge for the martyr Muhandis is coming at the hands of Iraqis — until the last soldier among you leaves,” it said.

On Tuesday, Nujaba head Akram al-Kaabi said pro-Iran groups had further unified their ranks to respond to the US.

“The International Resistance Regiments have been formed in order to execute a harsh, deliberate response to the American terrorist forces,” Kaabi said.

His deputy had earlier called for an urgent meeting to unite anti-American forces across Iraq.

“We will wage a war against the American presence in all parts of the region that we can reach,” said Nasr al-Shammary.