A fresh air strike hit pro-Iran fighters in Iraq early Saturday, as fears grew of a proxy war erupting between Washington and Tehran a day after an American drone strike killed a top Iranian general.

The killing of Quds Force commander Major General Qasem Soleimani in Baghdad on Friday was the most dramatic escalation yet in spiralling tensions between Iran and the United States, which pledged to send more troops to the region -- even as President Donald Trump insisted he did not want war.

America's allies in the Gulf could be on the front line of Iranian reprisals after the assassination of military commander Qasem Soleimani inflamed fears of a disastrous escalation, analysts say.

The current cycle of violence in Iraq must be stopped before it "spirals out of control," European Foreign Minister Josep Borrell warned Friday, after the US killed a top Iranian in Baghdad.

Yemen's pro-Tehran rebels, who control the capital Sanaa, called Friday for "swift reprisals" for the killing of senior Iranian commander Major General Qasem Soleimani in a U.S. strike in Baghdad.

Two Middle East airlines suspended flights to the Iraqi capital Friday as a protective measure after the U.S. killed a top Iranian commander in an air strike near Baghdad's airport.

The U.S. is deploying up to 3,500 more troops to the Middle East in a show of force, a Pentagon official said Friday, after an American drone killed a top Iranian general.

A U.S. drone carried out a "precision strike" to kill senior Iranian commander Qasem Soleimani and Iraqi paramilitary chief Abu Mahdi al-Muhandis on Friday, a U.S. defense official told AFP. 

"A precision drone strike hit two vehicles at Baghdad airport," the official said. 

Israel held emergency security talks Friday and Prime Minister Benjamin Netanyahu cut short a foreign visit as the Jewish state braced itself for fallout from the assassination of a top Iranian military commander in a U.S. air strike.

The State Department on Friday told US citizens to leave Iraq "immediately," after an American strike killed top Iranian commander Qasem Soleimani in Baghdad.

The Syrian government on Friday condemned the killing of top Iranian and Iraqi commanders in a US strike which was hailed by the opposition.

The strike outside Baghdad airport killed top Iranian commander Qasem Soleimani and the deputy chief of Iraq's pro-Iran paramilitary organisation, Abu Mahdi al-Muhandis.