BEIRUT--Islamic State fighters recaptured a critical hill near the besieged city of Kobani on Thursday, dealing a blow to Syrian Kurdish forces in what has been a seesaw battle for small patches of territory in and around the northern Syrian city.

The hill, which has changed hands repeatedly in the five-week siege of the city, fell again to Islamic State forces after hours of fighting with the Syrian Kurdish forces and the rebel Free Syrian Army, Khaled Barkal, vice president of Kobani's local government, said by phone from the city.

With the retaking of the hill, known as Tel Shair, the extremist group can now shell Kobani from the south, east and west, according to the Syrian Observatory for Human Rights, a monitoring group.

A small force of the Free Syrian Army has been fighting alongside Syrian Kurds in Kobani throughout the fighting for the mainly Kurdish city.

The hill, located 2 miles west of Kobani, was captured by Islamic State at the start of fighting last month before being retaken by Syrian Kurdish forces after the U.S. stepped up airstrikes last week.

U.S. attacks have killed 464 Islamic State fighters since the U.S.-led campaign against Islamic State expanded to Syria on September 23, the Observatory said Thursday. The strikes also killed 57 members of the al Qaeda-linked Nusra Front and 32 civilians, it said.

A day after a spokesman for the Kurdish militia fighting in Kobani said U.S. arms wouldn't be enough to prevent Islamic State from capturing the city, the government of northern Iraq's autonomous Kurdish region said Wednesday it would send within "a couple of days" up to 150 soldiers equipped with heavy weapons to join the fight.

There was no sign on Thursday that those soldiers had left Iraqi Kurdistan to travel through Turkey to Kobani.

Three U.S. C-130 cargo planes dropped 28 bundles of weapons, ammunition and medical supplies in northwestern Kobani on Monday morning in a bid to help the Kurds defend the city.

The Syrian Kurds have repeatedly warned the U.S. they require heavy weaponry to confront Islamic State, which is fighting with superior arms such as tanks and artillery.

The U.S. military's Central Command said its fighter jets and bomber aircraft had carried out four airstrikes near Kobani Wednesday and Thursday, destroying an Islamic State vehicle, command-and-control center and "fighting positions."

It said it had also destroyed two Islamic State oil-holding tanks near the city of Deir Ezzour in eastern Syria, as the U.S. and its Arab and Western partners carried out nine airstrikes against what it said were Islamic State assets in neighboring Iraq.

Mohammad Nour Alakraa in Beirut contributed to this article.

Subscribe to WSJ: http://online.wsj.com?mod=djnwires