A U.S. airstrike is believed to have killed the leader of the Islamic State affiliate in Libya, Pentagon officials said Saturday, in a mission that did not appear to be related to the terror attacks claimed by the group in Paris.

Pentagon press secretary Peter Cook said the strike took place on Friday and targeted Wisam al Zubaidi, also known as Abu Nabil al-Anbari, who commands what is the Islamic State’s strongest branch outside of Iraq and Syria, according to U.S. intelligence officials. The former Iraqi police officer was dispatched to Libya in 2014 by Islamic State leader Abu Bakr al-Baghdadi to build up the group’s affiliate there.

Before going to Libya, Zubaidi was a senior Islamic State operative in Iraq. Like Baghdadi, he spent time in a U.S. prison in Iraq after the 2003 U.S.-led invasion.

In a statement, Cook said that Zubaidi may have been the spokesman in a gruesome video that showed the killing of 21 Egyptian Christians on a beach in Libya this year.

Defense officials, speaking on the condition of anonymity to discuss details of the operation, said the attack involved two U.S. F-15 aircraft that struck a small compound outside of Derna, a militant stronghold in eastern Libya. Several other people were in the same building at the time of the strike, officials said.

The Islamic State’s flag is seen in an area of northern Iraq. An Iraqi who was sent to Libya to lead the group’s affiliate there may have been killed in an airstrike in the North African country on the night of Nov. 13, 2015, U.S. officials said. (AP)

While officials are still assessing results of the operation, the strike was believed to have killed Zubaidi. Officials said the attack had been planned for some time and was not linked to Friday’s violence in Paris, which killed at least 129 people and was among the worst terrorist attacks on Western soil since Sept. 11, 2001.

The Islamic State has asserted responsibility for the coordinated assaults in Paris.

Friday’s airstrike was the first time that the United States has struck an Islamic State operation outside of Iraq and Syria that U.S. officials believe is under the command and control of the core organization’s leadership.

Militants in places such as Afghanistan and Nigeria have affiliated themselves with or declared allegiance to the Islamic State, but U.S. officials think those groups’ operations are not directly linked to leaders in Iraq and Syria.

In Libya, the presence of Zubaidi, who headed Islamic State operations in central Iraq before traveling to North Africa, signaled a different level of connection, officials said. Since earlier this year, Islamic State militants have consolidated their control of Sirte, a coastal city in Libya now under the group’s harsh rule.

Intelligence officials say the Islamic State is a hybrid operation in Libya, led partly by foreign fighters and partly by Libyans with extremist sympathies or who have felt disenfranchised in the years after the 2011 war that ousted Moammar Gaddafi.

Senior militants in Libya appear to have drawn from the experience the group has acquired during its growth across Iraq and Syria, using many of the same propaganda and enforcement measures to attract followers and discipline the local population.

Derna, far to the east of Sirte, is not controlled by the Islamic State but has long been a haven for Islamists.

The Islamic State has been able to thrive in Libya in large part because of the country’s political instability four years after its revolution. Since last year, Libya has had two governments vying for resources and legitimacy. But neither is able to impose security across the vast desert nation or curb a sprawling array of militias, militant cells, smugglers and criminal groups.