A U.S.-led coalition bomber aircraft and a drone, as it is pictured from the Turkish border town of Akcakale last month, fly over the northern Syrian town of Tel Abyad. (Gokhan Sahin/Getty Images)

A U.S. drone strike has killed Tariq al-Harzi, a senior Islamic State militant in Syria, in an attack that took place a day after another American aircraft killed his brother, also an influential militant, in neighboring Iraq, the Pentagon said Thursday.

Navy Capt. Jeff Davis, a Pentagon spokesman, said the strike that killed Tariq al-Harzi occurred June 16 in Shaddadi, Syria. Davis said Harzi was a “senior leader” in the militant group who had orchestrated the movement of fighters into Iraq and Syria and helped to smuggle weapons from Libya.

“His death will impact ISIL’s ability to integrate foreign terrorist fighters into the Syrian and Iraqi fight as well as to move people and equipment across the border,” he said in a statement, using an acronym for the militant group.

Harzi, a Tunisian national, was wanted by the U.S. government for allegedly overseeing the recruitment of Europeans to fight with the Islamic State and helping the group mount suicide bombings in Iraq.

According to the State Department, Harzi also arranged a donation of $2 million from a Qatar-based Islamic State supporter in 2013.

The strike in northeast Syria came a day after another American drone killed Ali al-Harzi, Tariq’s brother, near the Iraqi city of Mosul. Ali al-Harzi was an Islamic State member but was also suspected of involvement in the September 2012 attacks in Benghazi, Libya, that killed U.S. Ambassador J. Christopher Stevens and three other Americans.

U.S. officials, who have struggled to locate militants behind those attacks, reportedly questioned Ali al-Harzi in Tunisia in 2012.

U.S. intelligence officials have vowed to bring those involved in the attack to justice. More than a dozen criminal complaints have been filed under seal in the Benghazi case.

In June 2014, Delta Force commandos seized Ahmed Abu Khattala in Libya and brought him to Washington, where he awaits trial in connection with the Benghazi attack. He has pleaded not guilty to multiple terrorism charges.

A U.S. defense official, speaking on the condition of anonymity to discuss a recent operation, said the two brothers were not working together at the time of their deaths.

Tariq al-Harzi, the older brother, was described as a more senior member of the Islamic State.

While U.S. officials have said that American and allied airstrikes have killed as many as 1,000 Islamic State militants a month, it has been more difficult to choke off the flow of foreigners into Iraq and Syria to fight with the group.

Adam Goldman contributed to this report.