Ambassadors from the 29 allies will gather at their Brussels headquarters at 3.00 pm (1400 GMT) with Secretary General Jens Stoltenberg expected to brief journalists afterwards.

US officials are due to give an update on the situation after Washington killed Qasem Soleimani, head of Iran's Middle East operations as commander of the Revolutionary Guards' Quds Force, in a US drone strike at Baghdad airport.

"The North Atlantic Council will address the situation in the region," a NATO official said.

"The secretary general decided to convene the meeting of NATO ambassadors following consultations with allies."

Stoltenberg had spoken by telephone with US Secretary of Defence Mark Esper since Friday's strike, but the killing of Soleimani surprised many of Washington's allies and triggered calls for de-escalation.

The situation has also deteriorated in Iraq, where lawmakers have called for the 5,200 US soldiers deployed there to leave.

NATO maintains a 500-strong training mission in Iraq, preparing local forces to take on Islamic State group extremists, but this would be in doubt if coalition forces pull out.

"The big issue is the future of the NATO mission in Iraq after the demand of the Iraqi parliament yesterday to remove US-led coalition and foreign forces. We have to see what we will do now," a NATO diplomat told AFP.

On Saturday, a NATO spokesman said the mission, which involves several hundred allied personnel, was continuing "but training activities are currently suspended".

Another diplomat said the alliance would have to "wait and see" how Baghdad responds in the coming days.

"From our point of view the parliament resolution is not binding. We take note of it, but have to wait what the government is going to do," the diplomat said.

"We still think that the presence of international troops in Iraq should be continued in order to prevent a resurgence of Islamic State. But we have to respect what the Iraqi government will eventually decide."

Tehran has vowed to avenge the commander, and US President Donald Trump has threatened "major retaliation" if any American targets are hit.

Britain, France and Germany issued a joint statement late on Sunday urging Iran to "refrain from further violent action or proliferation" and criticising the "negative role" Tehran played in the Middle East through Soleimani's forces.

Iran was also warned not to flout the 2015 nuclear deal, which Washington pulled out of in 2018, after announcing further steps away from the beleaguered accord.