A rocket attack on U.S.-led forces in northern Iraq killed a civilian contractor on Monday and injured a U.S. service member, the U.S. coalition in Iraq said, in the deadliest such attack in almost a year.

The rockets landed in and around a military air base operated by the coalition at Erbil International Airport.

The coalition spokesman tweeted on Tuesday that the dead contractor was not American, but did not elaborate. He said three 107 mm rockets had landed inside the base.

Of the nine other people hurt, eight were civilian contractors and one a U.S. service member, a coalition spokesman said. A U.S. official who declined to be named said the U.S. serviceman had concussion.

The attack, claimed by a little-known group that some Iraqi officials say has links with Iran, raises tensions as Washington explores some degree of détente with Iran.

It also comes just three weeks before a March 5-8 visit to Iraq by Pope Francis, which is due to include Erbil, the capital of Iraq’s Kurdish autonomous region.

U.S. Secretary of State Antony Blinken said the United States was “outraged” by the attack.

Powerful paramilitary groups aligned with Iran in Iraq and Yemen have launched attacks against the United States and its Arab allies in recent weeks, including a drone attack on a Saudi airport and a rocket attack on the U.S. Embassy in Baghdad.

Iraq’s government under Prime Minister Mustafa al-Kadhimi has sided with the United States but has found it hard to bring the groups under control.

Most of the incidents have caused no casualties, but they have kept up pressure on U.S. troops and U.S. allies in the early days of Joe Biden’s presidency.

Biden’s administration is weighing a return to the 2015 big power nuclear deal that aimed to curb Iran’s nuclear programme, which his predecessor Donald Trump abandoned in 2018.

Iran says it will only resume compliance with the deal if Washington lifts crippling sanctions. U.S.-Iran tension has often played out on Iraqi soil.

A U.S. drone strike that killed Iran’s military mastermind Qassem Soleimani in Baghdad in January 2020 sent the region to the brink of a full-scale confrontation.

A rocket attack on a base in northern Iraq last March killed three military personnel – one Briton and two Americans.

A group calling itself Saraya Awliya al-Dam claimed responsibility for the Erbil attack, saying it was aimed at the “American occupation” in Iraq, but provided no evidence.

In a statement, Blinken said he had contacted Kurdistan Regional Government Prime Minister Masrour Barzani to “pledge our support for all efforts to investigate and hold accountable those responsible”.