Beirut: At least 554 people have died since the Islamic State's (IS) advance on the northern Syrian Kurdish city of Kobane began in mid-September, the Syrian Observatory for Human Rights said Saturday.

At least 20 of those killed have been civilians who died in Kobane -- located on the border with Turkey -- and villages on its outskirts. Seventeen of those victims were executed by the Sunni militants, four of whom were decapitated.

Among the IS, around 300 fighters have died in clashes and airstrikes, as well as ambushes carried out by Kurdish militants. The toll also includes four suicide bombers who lost their lives in various attacks.

Among those fighting the IS on the ground, a total of 236 people have died, according to the Britain-based Observatory: 226 members of the Protection Units of the Kurdish People, nine rebels from other brigades that support the Kurdish militias and one volunteer.

The observatory has not ruled out the possibility of a higher casualty figure, noting the secretiveness of the combatants.

The IS began its assault on Kobane, one of Syria's three main Kurdish enclaves, Sep 16.

Since then, it has steadily continued its encroachment and currently controls 40 percent of the city.

Kurdish militias in recent hours have checked the extremists' advance within the town, which Saturday was the scene of airstrikes by the US-led coalition's warplanes.

The Protection Units of the Kurdish people Friday night launched several incursions into areas controlled by the Sunni militants on Kobane's eastern side, leading to intense fighting.

On Saturday, a double car bomb attack was carried out near a hospital in southwestern Kobane, although it is not yet known if anyone was killed or wounded.

The IS has declared a caliphate in the parts of Syria and neighbouring Iraq which are under its control.