A U.S. airstrike in Iraq has killed an Islamic State militant suspected of involvement in the 2012 attacks in Benghazi, Libya, that killed U.S. Ambassador J. Christopher Stevens and three other Americans, the Pentagon said Monday.

Col. Steve Warren, a military spokesman, said that Ali Awni al-Harzi, who U.S. officials believe acted as an intermediary for militant groups across the Middle East and North Africa, was killed in a strike in the northern Iraqi city of Mosul on June 15.

“His death degrades ISIL’s ability to integrate North African jihadists into the Syrian and Iraqi fight, and removes a jihadist with long ties to international terrorism,” Warren said, using another name for the militant group that controls a vast swath of Iraq and Syria.

Warren described Harzi, a Tunisian, as a “person of interest” in connection with the attacks in Benghazi, where militants overran a U.S. diplomatic facility on Sept. 11, 2012.

A U.S. defense official, speaking on the condition of anonymity to discuss the operation, said Harzi, whom he described as part of the group’s “middle management,” was in a vehicle when he was killed in a drone strike. The United States and allied nations have been conducting airstrikes against Islamic State militants in Iraq since last summer.

Harzi, 29, was designated a “global terrorist” in April by the State Department, which described him as a “Syrian-based Tunisian national who joined Ansar al-Sharia in Tunisia (AAS-T) in 2011.” It also said he was “a high-profile member known for recruiting volunteers, facilitating the travel of AAS-T fighters to Syria, and for smuggling weapons and explosives into Tunisia.”

Harzi and his brother Tariq, 33, were added to the United Nations terrorism list of al-Qaeda associates days before the State Department’s April designation. According to a U.N. Security Council statement, both brothers were said to be in Syria, with Iraq added as a “possible alternative location” as of March.

The U.N. statement said that in 2005, Ali Harzi was “detained and sentenced to 30 months imprisonment for planning terrorist attacks . . . in Tunisia.” It said he “planned and perpetrated the attack” against the U.S. mission in Benghazi.

After the Benghazi attack, Harzi is believed to have fled to Turkey, where he was arrested at an airport in late October 2012 and held for several days before being extradited to Tunisia. The FBI, which sought Harzi after a social-media post indicated involvement in the attack, reportedly questioned him in Tunisia in December 2012.

To the dismay of authorities in Washington, the Tunisian government released him the following month, citing lack of evidence.

A U.S. intelligence official said Harzi was suspected of playing a role in the attacks, but it’s unclear what exactly U.S. officials suspect he did.

U.S. officials have struggled to track down and prosecute suspects in the Benghazi incident, the first time a senior American diplomat had been targeted and killed in more than 30 years, in part because of ongoing instability in Libya. In 2014, U.S. Special Operations forces captured Ahmed Abu Khattala, a suspected ringleader in the attacks, in Libya. He has pleaded not guilty in a U.S. federal court to charges including murder and conspiracy.

Last March, immediately before the U.N. and State Department designations, the Tunisian National Guard issued an arrest warrant for Ali Harzi.

The U.N. listing for his brother, Tariq, called him “a dangerous and active member of al-Qaeda in Iraq in 2004, also active in facilitating and hosting members of Ansar al-Sharia in Tunisia in Syria.” The Obama administration has described al-Qaeda in Iraq as the precursor organization to the Islamic State, whose forces swept across northern Iraq a year ago, drawing the United States back into miltiary operations there.

Tariq Harzi was sentenced in absentia by a Tunisian court in 2007 to 24 years in prison for terrorist activities.

In January 2014, the State Department designated what it said were three separate Ansar al-Sharia groups, two in Libya and one in Tunisia, as foreign terrorist organizations.

The Tunisian group, it said, was founded in early 2011 and was “involved” in the September 2012 attack against the U.S. Embassy and American school in Tunis, days after the Benghazi attack in neighboring Libya. It described the Tunisian group as “ideologically aligned with al-Qaeda and tied to its affiliates,” including its North Africa branch, called al-Qaeda in the Islamic Maghreb.

Adam Goldman contributed to this report.