According to Turkey's Dogan news agency, some 3,000 civilians were trying to cross the border from Syria on Thursday, as the "Islamic State" (IS) militant group pushed ahead with its offensive.

IS fighters took control of some 21 villages near the Syrian Kurdish town of Kobane within 24 hours, according to the Britain-based Syrian Observatory for Human Rights. The offensive, from both east and west, began on Tuesday and was accompanied by heavy shelling.

A Syrian Kurdish militia in control of Kobane claimed its forces were resisting IS fighters advancing on the town with heavy weapons, tanks and mortars.

The local news website Welati reported a call by the authorities for people to join militia known as the People's Protection Units (YPG) - which until now were regarded as being among the most effective forces in fighting IS.

The Kurdish fighters also joined an offensive in neighboring Iraq, playing a role to open up safe passage for members of the Yazidi religious minority who were stranded on a mountain after fleeing IS. Earlier this year, the YPG said it had captured 13 villages near the majority Kurdish city of Qamishli from IS.

The Reuters news agency reported that leaders of the Kurdistan Workers' Party (PKK) were urging young people in Turkey to join the fight across the border.

"The youth of northern Kurdistan (in southeastern Turkey) should go to Kobane and take part in the historic, honorable resistance," read a statement on the PKK website.

rc/mkg (AFP, AP, dpa, Reuters)