KARKAMIS, TURKEY (AFP) - At least 10 more Turkish tanks on Thursday (Aug 25) crossed the border into Syria a day after pro-Ankara Syrian opposition fighters ousted militants from the town of Jarabulus, an AFP photographer said.

The tanks were set to join around a dozen others which had crossed the frontier on Monday in Operation Euphrates Shield, which Turkey says aims at ridding the border area of Islamic State in Iraq and Syria (ISIS) extremists and also Kurdish militia.

Turkish President Recep Tayyip Erdogan said on Wednesday that the offensive had expelled ISIS from the Syrian town of Jarabulus, and pro-Ankara rebels reported the militants had retreated south to Al-Bab.

The operation, the most ambitious launched by Turkey during the five-and-a-half-year Syria conflict, has seen Turkish special forces deployed on the ground and jet fighters striking ISIS targets.

They are supporting a ground offensive by hundreds of Syrian rebels who on Wednesday marched into Jarabulus and a neighbouring village after meeting little resistance.

It was not immediately clear if the deployment of the new tanks was aimed at securing Jarabulus or helping the rebels move into new territory.

But a Turkish official said on Wednesday that Ankara would "continue operations until we are convinced that imminent threats against the country's national security have been neutralised".

The official emphasised that the Syrian rebels were leading the way with "Turkey's main role to facilitate (the) advances".

The Hurriyet daily, citing military sources, said 100 ISIS militants had been killed in the offensive. It is not possible to independently verify the toll.

Some 1,500 Syrian fighters were involved in the offensive with 200 Turkish soldiers also on the ground, it added.

Jarabulus, a small town on the west bank of the Euphrates a couple of kilometres (miles) south of the border, had been held by ISIS militants since the summer of 2013.

But Mr Erdogan had also emphasised that the offensive was also aimed at People's Protection Units (YPG) Kurdish militia who have also been active in the area.

Turkey sees the YPG as a terror group bent on carving out an autonomous region in Syria.

Ankara's hostility to the YPG puts it at loggerheads with its Nato ally, the United States, which works with the group on the ground in the fight against ISIS.

But US Vice-President Joe Biden, visiting Turkey on Wednesday, made clear that Washington has strictly told the YPG not to move west of the Euphrates after recent advances.

"They cannot, will not and under no circumstances (will) get American support if they do not keep that commitment. Period," said Mr Biden.