Iran's supreme leader has said a missile attack on two US bases in Iraq was “not enough” — amid mounting fury in his country over the assassination of General Qasem Soleimani.

Ayatollah Ali Khamenei said the strikes were a “slap in the face” for America but stressed that it was more important for US troops to leave the region.

His remarks, less conciliatory than foreign minister Javad Zarif’s, were met with chants of “death to America” at a commemoration of the Qom protest, a key event leading up to 1979’s Islamic Revolution.

The military said last night’s attack lasted half an hour, from about 10.30pm. About 15 ballistic missiles were fired at the Al Asad airbase in Anbar province, western Iraq, and a base near Irbil in the semi-autonomous Kurdish region.

There were no US or British casualties, military sources said, despite claims on Iranian TV that “at least 80 terrorist US soldiers” had been killed. It was Iran’s most direct assault on America since the 1979 seizure of its Tehran embassy, but the strikes appeared to have been calculated to avoid escalating the crisis towards war.

They followed days of mourning for Soleimani, commander of the elite Quds Force in Iran’s Revolutionary Guard, who was killed in a drone attack at Baghdad airport last week. Despite mixed messages from Tehran, there were signs both Iran and the US were acting with caution.

Mr Zarif tweeted: “Iran took & concluded proportionate measures in self-defence under Article 51 of UN Charter, targeting base from which cowardly armed attack against our citizens & senior officials were launched.

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"We do not seek escalation or war, but will defend ourselves against any aggression.”

© Provided by Evening Standard Iraqi security forces find and collect the pieces of missiles (Anadolu Agency via Getty Images)

Donald Trump tweeted: “All is well!” Regarding casualties, he added: “So far, so good.”

Foreign Secretary Dominic Raab said: “We condemn this attack on Iraqi military bases hosting coalition, including British, forces.

© Provided by Evening Standard A man holds shrapnel from a missile launched by Iran on US-led coalition forces (Reuters)

"We urge Iran not to repeat these reckless and dangerous attacks, and instead to pursue urgent de-escalation.”

In pics: US and Iran tensions hit boiling point

Questions remained over whether the strikes were just an initial response. Former foreign secretary Sir Malcolm Rifkind told Talk Radio the Iranians had acted at the “mildest end of the spectrum” and either realised they were “weak” or were biding their time for “a more sinister response”.

Fred Fleitz, chief of staff to former US national security adviser John Bolton, told Today there could be “terrorist attacks by proxies, but I also think the Iranians are worried about how President Trump will respond”.

It comes as Hassan Rouhani, president of Iran, wrote on Twitter: "General Soleimani fought heroically against ISIS, Al Nusrah, Al Qaeda et al.

"If it weren’t for his war on terror, European capitals would be in great danger now. Our final answer to his assassination will be to kick all US forces out of the region."