The move means the SDF - which include the Kurdish YPG militia - has further consolidated recent gains around the rebel-held Syrian town of Azaz, the last before the border with Turkey.
Turkey, which considers the YPG to be a terrorist group, has warned Kurdish fighters in northern Syria they would face the "harshest reaction" if they tried to capture Azaz and has been shelling their forces for the past few days.
But YPG fighters appear now to be moving eastwards rather than north, the so-called Syrian Observatory for Human Rights monitoring group and a militant commander told Reuters, towards the front line with Daesh (ISIL) to the east of Azaz.
The Observatory's head, Rami Abdulrahman, said the SDF was now about 6 km away from Daesh territory southeast of Tal Rifaat.
The SDF was formed last year in an alliance with the YPG. Since then, the SDF has mostly fought Daesh and militant groups who are fighting to topple Syrian President Bashar al-Assad.
Syrian insurgents confirmed to Reuters that the SDF had taken significant parts of Tal Rifaat. Some said it had recaptured the whole town. Reuters could not independently verify the reports.
"You can consider that the whole town has been seized," one Syrian insurgent said.
A Syrian government offensive against militants, supported by Russian bombing and popular forces, has brought the army to within 25 km (15 miles) of Turkey's border and Kurdish-backed forces have exploited the situation, seizing ground to extend its presence along the frontier.
In the past 24 hours, SDF forces have also taken control of the village of Ayn Deqna -- cutting the main road north from Tal Rifaat to Azaz, and the village of Kefr Nasih -- just south-east of Tal Rifaat.