The Islamic State group shelled a Syrian border crossing with Turkey on Friday to try and capture it and cut off the embattled town of Kobani, a local Kurdish official and Syrian activists said.

The official, Idriss Nassan, said Islamic State fighters aim to seize the crossing in order to close the noose around the town's Kurdish defenders and prevent anyone from entering or leaving Kobani.

By mid-morning Friday, occasional gunfire and explosions that appeared to be rocket-propelled grenades and mortar shells could be heard from across the border in Turkey, and plumes of smoke were seen rising in the distance.

The Britain-based Syrian Observatory for Human Rights said the militants shelled several areas in Kobani, including the border crossing, which is the town's only gateway to Turkey.

Islamic State group this week pushed into Kobani for the first time since launching its offensive in the area in mid-September. The onslaught has forced more than 200,000 to flee the country across the border into Turkey and activists say the fighting over Kobani has killed more than 500 people.

"Daesh is doing all it can to take the border crossing point through the farmlands east of the city," Nassan said, using an Arabic acronym to refer to the Islamic State group. "They think there might be help (for the Kurdish militia) coming through the crossing so they want to control the border."

Meanwhile, members of the main Kurdish militia known as the Peoples Protection Units, or YPG, withdrew from a hill on the western outskirts of the town for tactical reasons, Nassan added, without giving further details.

The Observatory said the U.S.-led coalition launched airstrikes east and south of Kobani overnight. Nassan said an airstrike south of the town targeted the Al-Furat gas station, which is apparently under the control of the Islamic State group.

The Observatory said that after the airstrikes on Kobani intensified over the past days, targeting the Islamic State group's artillery and vehicles, the militants are now mostly firing mortar rounds and are using motorcycles to bring ammunition to their fighters on the front lines.