MURSITPINAR, Turkey – Islamic State fighters backed by tanks and artillery pushed into an embattled Syrian town on the border with Turkey on Monday, touching off heavy street battles with the town’s Kurdish defenders.

Hours after the militants raised two of their Islamic State group’s black flags on the outskirts of Kobani, the militants punctured the Kurdish front lines and advanced into the town itself, the Local Coordination Committees activist collective and the Britain-based Syrian Observatory for Human Rights said.

“They’re fighting inside the city. Hundreds of civilians have left,” said Observatory director Rami Abdurrahman. “The Islamic State controls three neighborhoods on the eastern side of Kobani. They are trying to enter the town from the southwest as well.”

The center of the town was still in Kurdish hands, Abdurrahman said. Kurdish officials could not be immediately reached for comment.

Since it began its offensive in mid-September, the Islamic State group has barrelled through one Kurdish village after another as it closed in on its main target – the town of Kobani, also known as Ayn Arab. The assault has forced some 160,000 Syrians to flee and put a strain on Kurdish forces, who have struggled to hold off the extremists even with the aid of limited U.S.-led airstrikes.

Capturing Kobani would give the Islamic State group, which already rules a huge stretch of territory spanning the Syria-Iraq border, a direct link between its positions in the Syrian province of Aleppo and its stronghold of Raqqa, to the east. It would also crush a lingering pocket of resistance and give the group full control of a large stretch of the Turkish-Syrian border.

After initially setting up positions to the east, south and west of the town, the Islamic State group shelled Kobani for days to try to loosen up the defenses. Just across the frontier in Turkey, the steady thud of artillery, sharp crackle of gunfire and plumes of smoke rising over the rooftops testified to the intensity of the fight all day Monday.

“ISIS is advancing further toward Kobani day by day,” said Ismet Sheikh Hassan, the defense chief for Kurdish forces in the area, using an alternative name for the Islamic State group. “ISIS is fighting with tanks and heavy weapons, and they are firing randomly at Kobani. There are many civilian casualties because of the shelling.”

The Syrian Observatory for Human Rights said about 20 Islamic State fighters managed to sneak into the eastern part of Kobani overnight, but were ambushed and killed by Kurdish militiamen.