Antony Blinken, the US secretary of state, expressed “outrage” after a rocket attack struck coalition forces in Iraq, killing one civilian contractor and injuring five others as well as wounding one American service member.

The attack in Erbil, the capital of the autonomous Kurdistan region of Iraq, could mark an early test for Joe Biden, the US president, as he tries to reset American foreign policy in the Middle East, particularly with regards to Iran.

The US has repeatedly blamed Iraqi militants backed by Iran for targeting American interests in Iraq with rockets and explosive devices.

“We are outraged by today’s rocket attack in the Iraqi Kurdistan Region. Initial reports indicate that the attacks killed one civilian contractor and injured several members of the Coalition, including one American service member and several American contractors,” Blinken said.

He added that he had “reached out” to Masrour Barzani, prime minister of Kurdistan Regional Government, “to discuss the incident and to pledge our support for all efforts to investigate and hold accountable those responsible”.

Colonel Wayne Marotto, the spokesperson for Operation Inherent Resolve, the 83-member coalition targeting the Isis extremist group, had earlier confirmed some details of Monday’s attack on Twitter but gave no indication of its origin.

“Initial reports that Indirect Fire landed on Coalition Forces in Erbil tonight. There was 1 civilian contractor killed, 5 civilian contractors injured and 1 US service member injured. More information to follow,” Marotto wrote.

Barham Salih, Iraq’s president, described the attack on Twitter as a “terrorist act” that represented a “dangerous escalation”.

Reuters reported that a group calling itself Saraya Awliya al-Dam claimed responsibility for the attack, saying it targeted the “American occupation” in Iraq. It provided no evidence for its claim. Experts described the group as a shadowy Shia militant movement linked to Iran-backed factions in Iraq.

“This is a reminder of how vulnerable US forces and US allies are to the militias in Iraq when they choose to act,” said Toby Dodge, a Middle East expert at the London School of Economics. “Certainly Biden is being reminded that the pressure points are still there and pressure can be applied, but probably more likely America’s allies [in Iraq] are being reminded how vulnerable they are.”

Former president Donald Trump took the US to the brink of war with Iran in January last year when his administration assassinated Qassem Soleimani, the Islamic republic’s most powerful commander. The Trump White House blamed Iranian-backed militants for a rocket attack on an Iraqi base hosting US troops that killed an American civilian contractor the month before.

The US subsequently reduced from 5,200 to 2,500 the number of troops in Iraq, where they have been training Iraqi forces and helping in the fight against Isis.

But sporadic attacks against American targets have continued, including rockets fired at the US embassy in Baghdad in December, as the Trump administration’s “maximum pressure” campaign against Iran ramped up tensions throughout the region.

Tehran backs militant groups across the region and Iranian-aligned militias have become increasingly powerful in Iraq in recent years.

The Biden administration was hoping to reduce regional tensions and has pledged to rejoin the 2015 nuclear deal if Tehran fully complies with the accord. The stand-off between Iran and the US erupted after Trump abandoned the nuclear agreement in 2018.

Kurdistan has been one of the more stable areas of Iraq since the 2003 US-led invasion of the country toppled Saddam Hussein.

Additional reporting by Katrina Manson in Washington