Syrian rebel forces broke through an ISIS siege around an opposition-held town in northwestern Syria on Wednesday, reopening their main road to the Turkish border, the Syrian Observatory for Human Rights said.

According to an opposition source and a monitoring group, ISIS fighters withdrew from frontlines with Syrian rebel forces north of Aleppo on Wednesday as the rebel groups besieged in the town of Marea had launched a counter attack against ISIS.

The sudden withdrawal from villages around the rebel-held town of Marea points to the pressure ISIS is feeling from offensives being waged by other enemies further east, the Syrian Observatory for Human Rights monitoring group said.

ISIS had managed to besiege the rebel-held town of Marea in a significant advance late last month, stranding thousands of civilians there and prompting a U.S.-led coalition to air drop weapons to rebels, rebel sources said.

Rebel fighters in Marea broke the siege on Wednesday when they captured the village of Kafr Kalbin on the road linking Marea with Azaz, 20 km (12 miles) to the northwest at the border with Turkey. The advance was preceded by a rebel statement saying they were uniting their ranks.

“It seems they (ISIS) can’t keep several fronts open at the same time. It is a strategic area, they were on the verge of entering Azaz,” Observatory Director Rami Abdulrahman said. The opposition source said ISIS had quickly pulled back from the area, and Free Syrian Army factions had filled the void.

FSA rebels fighting Islamic State north of Aleppo have received military assistance from states opposed to President Bashar al-Assad.

Their battle with ISIS is separate to one being waged further east by a U.S.-backed group, the Syria Democratic Forces, which includes the Kurdish YPG militia.