Syrian activists say Islamic State fighters have retaken a northern town along Syria's border with Turkey just days after losing it to rebel forces and allied militants.

The Britain-based Syrian Observatory for Human Rights and the Aleppo Today TV station say the IS extremists captured al-Rai early on Monday morning after intense fighting for the frontier town.

Al-Rai is strategically located on the border with Turkey, serving as the Islamic State group's access point to supply lines. It also sits along the road to the IS stronghold in Aleppo province.

IS lost the town on Thursday after an offensive by rebels and militant groups allied with them, including al-Qaida's branch in Syria known as the Nusra Front.