"I strongly condemn the terrorist attack targeting the residence of Iraqi Prime Minister al-Kadhemi," Biden said in a statement.

"I am relieved the Prime Minister was not injured and commend the leadership he has shown in calling for calm, restraint, and dialogue to protect the institutions of the state and strengthen the democracy Iraqis so richly deserve."

Kadhemi escaped unhurt when an explosives-packed drone struck his Baghdad residence early Sunday. But the attack marked a substantial escalation in the country's post-election turmoil.

The prime minister's office described the attack as a "failed assassination attempt", while Iraqi President Barham Salih called it an attempted "coup against the constitutional system." The strike was not immediately claimed by any group.

Biden said that "the perpetrators of this terrorist attack on the Iraqi state must be held accountable", condemning "in the strongest terms those using violence to undermine Iraq's democratic process".

He had instructed his national security team "to offer all appropriate assistance to Iraq's security forces as they investigate this attack and identify those responsible", the US leader added.

Later Sunday, the US State Department said Secretary of State Antony Blinken had spoken with Kadhemi, expressing relief the premier was unharmed and reiterating that the US-Iraq partnership was "steadfast".

He "underscored this attack was also an attack on the sovereignty and stability of the Iraqi state," State Department spokesman Ned Price said in the statement.