BEIRUT (AP) — Syrian opposition activists say dozens of Islamic State group members and their families have crossed into areas controlled by the extremists despite U.S. threats to bomb the convoy.

Saturday's announcement came hours after the U.S.-led coalition fighting IS said the 17-bus convoy of IS militants and their families that left the Lebanon-Syria border six days ago is still stranded in the Syrian desert.

Rami Abdurrahman, who heads the Britain-based Syrian Observatory for Human Rights, said dozens of fighters and civilians left the buses and drove into IS-held parts of the eastern province of Deir el-Zour in 12 civilian vehicles.

Opposition activist Omar Abu Laila, who is from Deir el-Zour and currently lives in Europe, gave an account similar to that of Abdurrahman adding that most of them have crossed.