The attack comes as tensions soar with the United States carrying out strikes on pro-Iran groups in Iraq and Syria amid the war in the Gaza Strip.

One of those killed was a commander of the Kataeb Hezbollah group in charge of military affairs in Syria, a member of the pro-Iran Iraqi group told AFP on condition of anonymity.

The source named the commander as Abu Baqr al-Saadi.

The security source also reported the deaths of two officials from Kataeb Hezbollah, which has taken part in the past in attacks on US forces in Iraq.

There was no immediate claim of responsibility for the drone strike.

But it came nearly a week after the United States struck 85 targets at seven different sites in Iraq and neighbouring Syria of Iranian and pro-Iranian forces.

Those strikes were in retaliation for an attack at the end of January on a base in Jordan that killed three US soldiers.

US and allied troops have been attacked more than 165 times in the Middle East since mid-October in a campaign waged by Iran-backed armed groups angered by US support for Israel in the war in Gaza.

The United States considers Kataeb Hezbollah a terrorist group, and officials in Washington had said they believed the group was behind the Jordan attack.

At the end of January the pro-Iran group said it was suspending its attacks against US forces.

Earlier a security source said the drone had fired three rockets at a 4X4 car in the east Baghdad neighbourhood of Machtal that targeted two officials from the Kataeb Hezbollah.

Another security official had said the vehicle carried an official from Hashed al-Shaabi, a coalition of mainly pro-Iran paramilitaries now integrated into Iraq's regular security forces.

An AFP photographer said security forces deployed in the neighbourhood barring access to it after the attack.

Later in the evening the carcass of a car was removed from the area.

The Hashed al-Shaabi has said that 16 of its fighters were killed in Friday's US strikes and 36 people wounded. The Syrian Observatory for Human Rights war monitor said at least 23 pro-Iranian fighters were killed in Syria.

"Targeting the Hashed al-Shaabi is playing with fire," the group's leader Faleh al-Fayyad warned on Sunday.

The United States and Iraq have opened talks on the future of the US-led troop presence in January, following a request by the Iraqi prime minister for a timetable for their withdrawal.

The United States has some 900 troops in Syria and 2,500 in Iraq as part of an international coalition against the Islamic State group.

Its troops in Iraq are deployed at the invitation of Baghdad, but those in Syria are deployed in areas outside government control.