KARKAMIS, Turkey: Turkey on Tuesday sent more tanks into Syria and sternly warned a Kurdish militia to withdraw from frontline positions, a day after pro-Ankara Syrian opposition fighters captured a key border town from extremists.
The tanks joined those which crossed the frontier on Wednesday in the so-called Operation Euphrates Shield, which Turkey says aims at ridding the northern Syrian border area of both ISIS extremists and Kurdish militia.
Turkish President Recep Tayyip Erdogan said on Wednesday that the offensive had expelled ISIS from the Syrian town of Jarablus, and pro-Ankara rebels reported the extremists had retreated south to the town of Al-Bab.
But Defense Minister Fikri Isik warned the Kurdish People's Protection Units (YPG) militia -- who also had designs on Jarablus -- to move back east across the Euphrates or also face intervention from Turkey.
The new contingent of tanks roared across a dirt road west of the Turkish border town of Karkamis, throwing up a cloud of dust in their wake before crossing the border, an AFP photographer said.
They were then followed by around 10 armored vehicles.
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 Jarablus and a neighboring village after meeting little resistance.
- 'Up to 15,000 troops' -
It was not immediately clear if the deployment of the new tanks on Thursday was aimed at securing Jarablus 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 neutralized."
The well-connected columnist of the Hurriyet daily, Abdulkadir Selvi, said the aims of the operation included creating a security zone free of "terror groups" and limiting the advances of Kurdish militia.
He said 450 members of the Turkish military had been on the ground on the first day of the offensive but this number could rise to 15,000.
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.
State-run news agency Anadolu said one rebel fighter was killed but the Turkish armed forces sustained no losses.
- 'Every right' -
Jarablus, a small town on the west bank of the Euphrates a couple of kilometers (miles) south of the border, had been held by ISIS extremists since the summer of 2013.
Turkey has emphasized that the offensive was also aimed at the YPG, who Ankara sees 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 or risk losing American support.
Turkish Defense Minister Fikri Isik told NTV television there was so far no evidence of any withdrawal and Turkey reserved the right to strike the YPG if it failed to move.
"If this withdrawal doesn't happen, Turkey has every right to intervene," Isik added.
"They have not yet withdrawn... Turkey will be following, moment by moment," Isik said, adding the withdrawal was promised within a week.
A spokesman for the US-led coalition against ISIS tweeted that the "main element" of the Syrian Kurdish forces had already moved east although some remained for clean-up operations.
- Selfies on the way -
Ankara has in the past been accused of turning a blind eye to the rise of ISIS but hardened its line in the wake of a string of attacks -- the latest a weekend bombing on a Kurdish wedding in the city of Gaziantep that left 54 people dead, many of them children.
The Jarabulus operation proceeded at lightning speed with the town captured from ISIS just 14 hours after it was launched.
The speed of the advance stood in stark contrast to the long, grinding battles it had taken for Kurdish forces to recapture towns from ISIS in northern Syria, such as Kobane and Manbij.
Television pictures showed the Syrian fighters walking into an apparently deserted and abandoned Jarablus unchallenged and newspapers published pictures showing that the rebels even had time to take selfies along the way.
The apparent efficiency of the operation also marked a major boost for the Turkish army whose reputation had been badly tarnished by the failed July 15 coup against Erdogan staged by rogue elements in the armed forces.