Islamic State militants battling for control of the Syrian border city of Kobani ramped up their offensive Thursday, re-taking ground west of the city where the U.S. made a crucial supply drop to Kurdish forces on Monday.

A Fox News crew in the area has been told that ISIS has advanced on three different fronts in the center of Kobani against Kurdish defenders. There is now little open land around the city that the Kurds control, making future airdrops difficult.

Turkish President Tayyip Erdogan said Thursday that a unit of 200 Kurdish Peshmerga forces from Iraq will be coming to Kobani to help in the fight against ISIS, but there is no word on when the troops will arrive. They are reported to bring heavy weaponry and artillery that is sorely needed to push back the militant advances.

An Associated Press journalist on the Turkish side of the border said heavy machine gunfire could be heard from Kobani, which is also known as Ayn Arab, on Thursday.

"The fighting has been ongoing since last night on the eastern and southern fronts. It is some of the longest clashes in Kobani," said Kurdish activist Farhad Shami by telephone from the town. "The fighting usually only takes place at night."

Shami added that Kurdish fighters withdrew from the Tel Shair hill that overlooks parts of Kobani.

The Observatory said Islamic State fighters captured the hill, closing in on the town from the west. It said Islamic State fighters are also trying to advance from the eastern side of the town, saying there were casualties on both sides.

The hill was captured by the Kurds from Islamic State fighters earlier this month.

Idris Nassan, deputy minister for foreign affairs in a Kurdish civil administration controlling Kobani, said that although Islamic State fighters moved onto Tel Shair hill, the heavy fighting there was ongoing.

"Kobani has been witnessing fierce clashes since last night. It was one of the bad nights," Nassan said.

The news of the offensive came as the Britain-based Syrian Observatory for Human Rights, which relies on a network of activists on the ground, reported that 553 people have been killed since the airstrikes began on Sept. 23, including 32 civilians. The civilians included six children and five women.

The group said it has documented the deaths of 464 fighters with the Islamic State group, adding that the real number could be much higher. Another 57 fighters with the Al Qaeda-linked Nusra Front were killed in airstrikes on the northern province of Aleppo and Idlib, the Observatory said.

Many of the Islamic State fighters have been killed in or near Kobani, the target of a massive jihadi offensive since mid-September. ISIS fighters have captured dozens of surrounding Kurdish villages and forced more than 200,000 people to flee for safety in neighboring Turkey.

Earlier this week, The U.S. Central Command said its forces have conducted more than 135 airstrikes against Islamic State militants in and around Kobani, killing hundreds of fighters.

"Combined with continued resistance to ISIL on the ground, indications are that these strikes have slowed ISIL advances into the city, killed hundreds of their fighters and destroyed or damaged scores of pieces of ISIL combat equipment and fighting positions," Central Command said in a statement.

U.S. Central Command said American forces continued to hit ISIS terrorists in Syria and Iraq on Wednesday and Thursday.

In Syria, four airstrikes near Kobani destroyed ISIS fighting positions, a vehicle and a command center. In Iraq, four airstrikes near the Mosul Dam hit four ISIS units and a vehicle. ISIS fighting positions and buildings were also targeted in Baiji and Fallujah.

The Observatory, meanwhile, reported four coalition airstrikes on oil wells in the Jafra field in the eastern Syrian province of Deir el-Zour late Wednesday. The Local Coordination Committees, an activist group, also reported the airstrikes in areas held by the Islamic State group.

Fox News’ Greg Palkot and The Associated Press contributed to this report.