The al-Qaida breakaway group that seized much of Iraq’s northern city of Mosul has encircled the city of Deir el-Zour across the border in Syria, activists said Wednesday.

“They have surrounded the city. There are no entrances or exits left for people to flee,” said a Syrian activist in the region who has contacts inside Deir el-Zour and who uses the name Salar. The information was confirmed by a second activist who uses the name Abu Abdullah, and who is based near Deir el-Zour.

The city, which straddles the Euphrates in the northeastern corner of Syria, is one of the oil-rich region’s last strongholds of resistance to the Islamic State. […]