A U.S. Air Force photograph shows a MQ-1 Predator unmanned aircraft. (REUTERS/U.S. Air Force/Lt Col Leslie Pratt/)

U.S. aircraft destroyed a car carrying “core al-Qaeda” members in northwestern Syria, Tuesday night, according to Pentagon officials. It is the second strike against the group’s affiliate in Syria in less than 72 hours.

According to a senior U.S. defense official, who requested anonymity to discuss an operation that had yet to be publicly announced, it is unclear if the strike eliminated any leadership figures. According to local news reports, the strike was carried out by a drone in Idlib city and killed five members of the al-Qaeda offshoot in Syria, known as Jabhat al-Nusra.

On Sunday a U.S. airstrike targeted Abu Firas al-Suri, a spokesman for al-Nusra. Al-Suri had deep ties to the original elements of al-Qaeda in Afghanistan, having fought along side Osama Bin Laden in the 1980s and 1990s. Pentagon Press Secretary Peter Cook described those ties when explaining the rationale for the strike. The Pentagon is still working to confirm al-Suri’s death.

According to the defense official, at least 20 other people were killed in the Sunday strike that targeted a meeting between al-Nusra and another Islamist group in the village of Kafr Jales in Idlib province.

The strike was considered “counter-terror” in nature and conducted unilaterally, according to the official, hence it was absent from the daily airstrike reports released by the U.S.-led coalition mission against the Islamic State.

The U.S. has gone after al-Qaeda’s affiliate in Syria in the past, including elements of the Khorasan Group — a cell within al-Nusra that planned external attacks against the West.

The Pentagon, for the most part, has refrained from striking al-Nusra. In July, U.S. airstrikes targeted the group after they overran a small contingent of U.S.-backed rebels that had been recently sent back into Syria following the completion of their Pentagon-led training course.

Al-Nusra is well established in Idlib province and other parts of western Syria and has often fought alongside opposition groups that are considered more moderate by the United States and some of its allies.

Zakaria Zakaria in Istanbul contributed to this report