A drone strike believed to have been carried out by the United States in northwestern Syria killed a prominent Tunisian extremist, a monitor said Tuesday.

The strike conducted Monday in the opposition-held province of Idlib killed Sayyaf al-Tunsi, said the Syrian Observatory for Human Rights.

“The drone targeted the vehicle of the Hurras al-Deen leader in Idlib, killing him,” said Observatory chief Rami Abdel Rahman.

Hurras al-Deen is a relatively small but powerful armed group led by al-Qaeda loyalists.

It is a rival of Hayat Tahrir al-Sham, an alliance of extremist factions dominated by former members of al-Qaeda’s ex-Syria affiliate Jabhat al-Nusra -- although the two groups cooperate at times.

Sayyaf al-Tunsi was former Nusra leader who was sidelined over his alleged responsibility for the 2015 massacre of 20 Druze villagers in Idlib Province.

There was no immediate confirmation of the strike from the United States, nor the coalition it leads in the region to fight against ISIS.

Rami Abdel Rahman said Tunsi’s car was targeted by a so-called “Ninja” R9X missile, a modified Hellfire on which the explosive head is replaced with blades to minimize “collateral damage.”