Islamic State fighters have re-entered the Syrian town of Kobani and are battling Kurdish militia, a group monitoring the war reported on Thursday.
The town at the Turkish border was captured by Kurdish forces from Isis in January after months of fighting.
The attack by Islamic State fighters on Kobani, also known as Ayn al-Arab, began overnight with a car bomb attack near the border crossing between the town and Turkey, the UK-based Syrian Observatory for Human Rights said.
Dozens of people have been killed or wounded in the bomb attack and fierce clashes, it said.
“IS detonated a suicide bomb in the area near the border crossing with Turkey, killing at least five people,” said the observatory director, Rami Abdel Rahman.
“Fierce clashes erupted afterwards in the centre of the town and there are bodies lying in the streets,” he added, without giving a specific toll.
He said fighting was still raging on Thursday morning.
A Kurdish YPG militia official told Reuters that a car bomb had exploded in Kobani, near the Turkish border gate, on Thursday as Isis militants staged an attack from three sides of the town.
Isis battled for four months to seize Kobani, but Kurdish fighters – backed by US-led air strikes – secured control of the border town in January in a symbolic defeat for the jihadists.
Thousands of people who fled Kobani across the border to Turkey have returned to the town since the siege.
Welat Omer, a doctor in Kobani, told Reuters that around 60 to 70 people had been wounded in the latest attacks, many of them women and children.
In recent weeks, forces of the Kurdish People’s Protection Units (YPG) have advanced from Kobani in Aleppo province into neighbouring Raqqa province, the Isis stronghold.
Isis fighters were also reported to have wrested areas of the northeastern Syrian city of Hasaka from government control in fighting overnight, although a Syrian military source denied the report, saying the army had repelled the attack.