Iran fired more than a dozen ballistic missiles in the early hours of Wednesday, officials in Washington and Tehran said.

Iran said it was responding to the US killing of top Iranian general Qasem Soleimani last week, warning it would hit back even harder if Washington responded.

- 'All is well' -

"All is well!" US President Donald Trump's tweeted. "Assessment of casualties & damages taking place now. So far, so good!"

He would be making a statement on Wednesday morning, he added.

- 'Refrain from further violence' -

NATO chief Jens Stoltenberg said: "I condemn the Iranian missile attacks on US and coalition forces in Iraq. NATO calls on Iran to refrain from further violence."

A NATO official said none of its troops in Iraq had been hurt in the strikes.

- 'Resounding blow' -

Prime Minister Benjamin Netanyahu, who has described Soleimani as Iran's "terrorist-in-chief", made it clear Israel would strike back if attacked.

"Anyone who attacks us will receive a resounding blow," he warned.

- 'Urgent de-escalation' -

Britain's Prime Minister Boris Johnson told parliament: "Iran should not repeat these reckless and dangerous attacks but should instead pursue urgent de-escalation."

Earlier, Foreign Secretary Dominic Raab warned that another war in the Middle East would only benefit the Islamic State group "and other terrorist groups".

- 'No-one's interest' -

The European Union's foreign policy chief Josep Borrell said the attack was yet another example of "escalation and increased confrontation".

"It is in no-one's interest to turn up the spiral of violence even further," he added, warning that the crisis was hampering the fight against Islamic State.

EU foreign ministers will hold emergency talks on the Iran crisis Friday to discuss what the bloc can do to reduce tensions.

- 'Restraint and responsibility' -

French Foreign Minister Jean-Yves Le Drian said in a statement: "The priority is more than ever for a de-escalation.

"France remains determined to work to ease tensions and is in contact with all the parties to encourage restraint and responsibility."

- 'Violation of sovereignty' -

The Iraqi prime minister's office said it had received an official warning from Iran just before the missile launches.

Iran had told premier Adel Abdel Mahdi that "the strike would be limited to where the US military was located in Iraq without specifying the locations", said the statement from his office.

"Iraq rejects any violation of its sovereignty and attacks on its territory," the premier's office added.

- Civilian flights rerouting -

In the wake of the Iranian attack, a number of airlines said they were avoiding Iranian and Iraqi airspace.

The US Federal Aviation Administration said it was banning US-registered carriers from flying over Iraq, Iran and the Gulf.

Its Russian counterpart, the Federal Air Transport Agency, recommended airlines avoid the air space over Iran, Iraq and the Persian and Oman Gulfs.