The Britain-based Syrian Observatory for Human Rights says Abdul Mohsen Abdallah Ibrahim al-Charekh, a Saudi better known as Sanafi al-Nasr, was killed Thursday in an airstrike near the northern Syrian town of Dana.
The Observatory's chief Rami Abdurrahman said today it was not clear if al-Charekh was killed by US or Russian warplanes.
Jihadi activists on social media say he was killed by a US drone strike.
Al-Charekh, the alleged leader of al-Qaida's operations in Syria, was one of six men that the UN Security Council imposed sanctions on last year.