Turkish-backed Free Syrian Army fighters are seen in Khaldieh village in eastern Afrin, Syria March 10, 2018. REUTERS/Khalil Ashawi

BEIRUT (Reuters) - Turkish forces have reached the outskirts of the town of Afrin after a weeks-long campaign against a Kurdish militia in northwest Syria, the Syrian Observatory for Human Rights war monitoring group said on Saturday.

Turkey and allied Syrian rebel groups it supports are advancing on the town from the east under intense bombardment, the Britain-based Observatory said.

Ankara launched its offensive in the Afrin region on its border in January, aiming to drive out the Syrian Kurdish YPG militia, which it sees as an extension of the PKK group that has fought a three-decade insurgency inside Turkey.

During the campaign it has managed to gain control over all the Afrin region’s border areas with Turkey, including several small towns and a large number of villages.

Despite being rivals with the Syrian government and having clashed with the Syrian army at times in the war, the YPG has asked Damascus to help it repel the Turkish assault.

Last month, pro-Syrian government militias entered Afrin region to back up the YPG, but their deployment did not deter Turkey despite the possibility of a wider escalation in the war, and it continued its campaign.

Afrin is separated from a much larger area held by Syrian Kurdish forces further east along the border with Turkey, including large swathes of land captured from Islamic State with support from the United States.

On Friday, Turkish President Tayyip Erdogan said the Turkish army would soon enter Afrin. He also vowed to sweep Kurdish fighters from the length of the border.