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CNN  — 

A US civilian contractor was killed Friday in a rocket attack on a base near Kirkuk, Iraq, where US service members and civilian contractors were located, an Operation Inherent Resolve spokesman confirmed.

K1 military base, which houses US troops in Kirkuk province in northern Baghdad, was attacked by several katyusha rockets on Friday, according to the Iraqi military.

Several US and Iraqi military members were wounded in the attack, which happened at 7:20 p.m. Iraq time, OIR spokesman Col. Myles B. Caggins III said. A US official told CNN that “less than a handful” of Americans were wounded, and it’s believed some have already returned to duty. The Iraqi military said only one Iraqi security officer was injured in the attack.

The US is now trying to determine who was responsible for the attack, officials said. The US has so far not disclosed the identity of the contractor killed, or the company they worked for. Iraqi security forces are leading the response and investigation, Caggins said.

US Secretary of Defense Mark Esper recently had asked Iraq to help prevent attacks on US personnel that both countries have attributed to groups backed by Iran.

Esper spoke with Iraqi Prime Minister Adil Abdul-Mahdi earlier this month.

“On the call, Secretary Esper reiterated United States support for a secure and sovereign Iraq and the people of Iraq. He also called on our Iraqi partners to continue to assist in preventing attacks on US and coalition personnel and facilities in the country,” Pentagon spokesperson Cmdr. Sean Robertson told CNN in a statement.

US officials have grown increasingly concerned about a series of rocket attacks on military installations in Iraq where US and coalition personnel are stationed.

One US official told CNN that the US sees similarities between Friday’s attack and past attacks that have been linked to a Shiite militia in Iraq believed to be backed by Iran’s Islamic Revolutionary Guard Corps.

“There are a lot of similarities to some of the other 10 rocket attacks in the last two months which we have linked to Iranian-backed militias. We are looking into a possible link to Kataib Hezbollah in particular,” the official said.

UPDATE: This story has been updated to reflect that the Iraqi military amended its original statement with new information stating that the base was hit by katyusha rockets, not mortar rounds.