Iran fired more than a dozen ballistic missiles overnight Tuesday-Wednesday, officials in Washington and Tehran said.

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

- Trump: '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 Wednesday morning, he added.

- '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 Foreign Secretary Dominic Raab called on Iran to end its attacks.

"We condemn this attack on Iraqi military bases hosting Coalition -- including British -- forces," he said, urging Iran not to repeat them but instead to "pursue urgent de-escalation.

"A war in the Middle East would only benefit Daesh and other terrorist groups," he added, referring to the Islamic State group. Britain's defence ministry said there had been no British casualties.

- '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. He too warned 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.

- 'Violation of... sovereignty' -

Iraq's prime minister's office said it had received an official message from Iran warning it of the missile attack just before it happened.

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.