Mourners escort a vehicle carrying the coffin of Aziz Guler, during a funeral ceremony in Gazi neighbourhood of Istanbul on Sunday. According to the local media, left-wing activist Guler was killed on September 21 in a landmine explosion while he was fighting for the Syrian Kurdish YPG militia against Islamic State militants in northern Syria.

Reuters/Amman

A bomb placed on a motorcycle exploded on Sunday in a Kurdish-held Syrian town along the Turkish border, killing at least three and wounded 20 others, a monitor said.

The UK-based Syrian Observatory for Human Rights said a huge blast was heard when the bike blew up in the centre of Tel Abyad, a town captured by Kurdish-led forces from Islamic State militants in June with help from US-led air strikes.

The target was a checkpoint of Kurdish YPG forces, another source said.

Although Kurdish forces have reversed the momentum of the ultra-hardline Islamist militants along the Turkish border, and pushed them from areas in the northern provinces, Islamic State fighters continue to carry out lighting attacks, such as ambushes and suicide car bombings.

Last week Islamic State attacked Kurdish forces and a coalition of Arab tribes in Ain Issa, a town further south in Raqqa province also seized by the Kurdish-led forces last summer and within 50 km of Raqqa city, Islamic State's de facto capital.

The YPG fighters, who have emerged as the most credible ally of the US-led campaign on the ground in Syria, recently joined forces with several Arab tribes in a new US-backed coalition called the Democratic Forces of Syria.

They seized over a week ago several Islamic State-held villages in Hasaka province, the most important of which was al Houl, in a push further south into Islamic State-controlled territory.

Separately, the Syrian army which has also been fighting Islamic State across northern Syria said on Sunday it had taken control of a series of heights known as the Hayel in the southern part of the ancient city of Palmyra in central Syria.

The Syrian army, backed by some of the heaviest Russian attacks on the hardline Islamist group, has been waging a major offensive to recapture the historic city that was seized last May.

The army also said on Sunday it was closing in on the town of Maheen in the southwest of Homs which was captured by militants from government forces early this month.

These areas have seen intensified Russian air bombardments in recent days, say rebels. The Russian military has also said they have intensified raids against militant hideouts across Syria.