BEIRUT — Activists say fighters from the Islamic State of Iraq and the Levant have taken control of Syria’s largest oil field, near the border with Iraq.

The Britain-based Syrian Observatory for Human Rights says the extremist group captured al-Omar oil field in eastern Deir el-Zour province on Thursday after fighters belonging to a rival group, the al-Qaeda-linked Nusra Front, left without firing a bullet.

The al-Omar field has changed hands several times in the course of Syria’s three-year conflict. The Nusra Front and several other Islamic factions captured it from forces loyal to President Bashar Assad in November.

The Islamic State of Iraq and the Levant has seized a large expanse of territory in Syria and neighboring Iraq, and has declared the establishment of an Islamic state astride the border.

Copyright 2014 The Associated Press.