"I don't think you can convince Iraq with threats, but with arguments," Maas told Deutschlandfunk radio, warning that years-long efforts to rebuild Iraq "could all be lost" if the situation escalates.

Trump earlier vowed to hit Iraq with sanctions "like they've never seen before" if US troops are forced to leave the country.

The threat came after Iraqi lawmakers voted on Sunday to request the government end an agreement with a US-led international coalition to fight the hardline Islamist group IS in the region.

Tensions have soared following the killing of top Iranian general Qasem Soleimani by a US drone strike in Baghdad on Friday.

A furious Tehran has since announced a further step back from its commitments to the 2015 nuclear accord, leaving the future of the hard-fought pact in doubt.

European leaders have called for an urgent de-escalation of tensions, but Maas admitted that US Secretary of State Mike Pompeo had hoped for more full-throated backing from allies.

"Apparently he wasn't too happy that we didn't 100 percent support America's actions," Maas said after Pompeo spoke by phone with his German, French and British counterparts.

Maas said it was important that the European Union presented a united stance so it could play a meaningful role in helping to cool tempers.

"Our own security interests are massively affected by the fight in Iraq against international terrorism, against IS, so we have a responsibility here," he said.

"I think it's necessary that the EU foreign ministers quickly convene in Brussels to coordinate a European position."

He also said Germany, France and Britain would decide this week how to react to Iran's decision to forego the limit on enrichment it had pledged to honour in the nuclear agreement.

"We can't just accept this without responding," Maas said.

"It certainly doesn't make things easier and it could be the first step towards the end of the deal and that would be a great loss."