An American contractor was killed and five U.S. troops and a second U.S. contractor were wounded when a suspected Iranian-linked drone attacked a coalition military base in northeast Syria late Thursday, the Pentagon said in a statement.

 The Pentagon said it launched retaliatory airstrikes on facilities used by groups affiliated with Iran's Islamic Revolutionary Guard Corps.

"The U.S. does not – does not, I emphasize – seek conflict with Iran, but be prepared for us to act forcefully to protect our people," President Joe Biden said Friday, addressing the attack during a visit to Canada. "That's exactly what happened last night."

There was no immediate reaction from Iran's government. Iran’s diplomatic mission to the United Nations did not immediately respond to a request for comment.

The Syrian Observatory for Human Rights, a London-based war monitoring group, said the U.S. airstrikes killed eight pro-Iranian fighters in Syria.

U.S. Defense Secretary Lloyd Austin said in a statement that two of the wounded U.S. service members were treated at the base. The three additional service members and the American contractor were evacuated to medical facilities in neighboring Iraq.

Austin said the airstrikes were conducted in a response to Thursday's attack as well as a series of recent attacks that have targeted coalition forces in Syria. 

Biden extended his "heart and deepest condolences" to the family of the deceased American and wished a speedy recovery to the wounded. "I'm also grateful for the professionalism of our service members who so ably carried out this response," Biden said.

There are about 900 U.S. troops and an unknown number of American military contractors in Syria, a presence that is maintained to apply pressure to the remnants of the Islamic State militant group and to try to limit Iran's influence in Syria. It is not the first time Biden has authorized strikes against pro-Iranian fighters in Syria.

Biden's first military action as president, in late February 2021, was to order airstrikes against Iranian-backed militias in Syria in response to attacks on U.S. and coalition military personnel in Iraq. Iranian proxy groups have been launching attacks on U.S. troops in Syria and Iraq for several years, but the pace escalated after an American drone strike in January 2020 killed Maj. Gen. Qasem Soleimani, a top Iranian commander, while he was in Baghdad visiting with senior Iraqi security officials. 

The U.S. Congress is considering repealing bills from 1991 and 2002 that allowed for the use of force against Iraq's government during the Iraq War, the 20th anniversary of which was marked Monday. This bill is known as the authorization of military force, or AUMF. Some lawmakers also want to repeal or update a separate 2001 AUMF that sprung from President George W. Bush's "global war on terror" and the invasion of Afghanistan after 9/11. That 2001 authorization has been stretched to allow the U.S. to target militant groups in Syria, Pakistan, the Philippines and beyond.