Pompeo called officials worldwide to discuss the attack, which was praised by US President Donald Trump's Republicans and close ally Israel, but elsewhere met with sharp warnings it could inflame regional tensions.

"I spent the last day and a half, two days, talking to partners in the region, sharing with them what we were doing, why we were doing it, seeking their assistance. They've all been fantastic," Pompeo said in an interview with Fox News.

"And then talking to our partners in other places that haven't been quite as good. Frankly, the Europeans haven't been as helpful as I wish that they could be," he said.

US officials said Soleimani, who had been blacklisted by the US, was killed when a drone hit his vehicle near Baghdad's international airport.

Following the assassination, EU foreign affairs chief Josep Borrell called on all involved actors "to exercise maximum restraint and show responsibility in this crucial moment."

Meanwhile French President Emmanuel Macron urged those involved to act with "restraint" while British Foreign Secretary Dominic Raab said de-escalation would be key.

"The Brits, the French, the Germans all need to understand that what we did, what the Americans did, saved lives in Europe as well," Pompeo said.

"This was a good thing for the entire world, and we are urging everyone in the world to get behind what the United States is trying to do to get the Islamic Republic of Iran to simply behave like a normal nation," he added.

Pompeo said earlier in the day that Soleimani was planning imminent action that threatened American citizens when he was killed in the strike.