Turkey sent a fresh contingent of tanks Thursday into Syrian territory, a day after a lighting offensive by hundreds of Syrian rebel fighters -- backed by Turkish tanks, war planes and special forces -- took the Syrian town of Jarabulus, ending over three years of jihadist control.
Turkey says Operation Euphrates Shield -- its most ambitious offensive of the five-and-a-half year Syrian civil war -- is aimed at ridding the northern Syrian border area of both Islamic State (IS) extremists and the Kurdish militia vehemently opposed by Ankara.
Defence Minister Fikri Isik warned the Kurdish Democratic Union Party (PYD) and its People's Protection Units (YPG) militia -- who also had designs on Jarabulus -- to move back east across the Euphrates or also face intervention from Turkey.
Hours later, Turkish artillery shelled targets of the PYD inside Syria, the state-run Anadolu news agency said, saying the group had violated a deal with the United States to stop advancing.
It quoted security sources as saying that the Turkish military would continue to intervene against the PYD until it began to retreat.
The Hurriyet daily said the PYD elements had been identified by a Turkish drone 10 kilometres (six miles) north of the Syrian town of Manbij.
The group of PYD elements was then fired on by Turkish Firtina howitzers from inside Turkey, it said. The group was "eliminated", it added, without giving further details.
- 'Every right' -
US Secretary of State John Kerry was due to meet his Russian counterpart Sergei Lavrov in Geneva Friday morning for talks expected to focus heavily on the situation in Syria.
Successive rounds of international negotiations have failed to end the Syria conflict, which has killed more than 290,000 people and forced millions to flee their homes.
Moscow and Washington support opposite sides in the conflict, which erupted in 2011 after President Bashar al-Assad's regime unleashed a brutal crackdown against a pro-democracy revolt.
Turkey sees the PYD and YPG militia as terror groups bent on carving out an autonomous region in Syria and acting as the Syrian branch of its own outlawed Kurdistan Workers' Party (PKK).
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Ankara's hostility to the YPG also puts it at loggerheads with the United States, which works with the group on the ground in the fight against IS.
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.
Turkey's defence minister 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 said. "Turkey will be following, moment by moment."
A spokesman for the US-led coalition against IS tweeted that the "main element" of the Syrian Kurdish forces had already moved east although some remained for clean-up operations.
- 'Mindset change' -
Jarabulus, a small town on the west bank of the Euphrates a couple of kilometres south of the border, had been held by IS jihadists since the summer of 2013.
Around 10 Turkish tanks roared across a dirt road west of the Turkish border town of Karkamis Thursday but it was not clear if the deployment was aimed at securing Jarabulus or helping the rebels move into new territory.
The well-connected columnist of the Hurriyet daily, Abdulkadir Selvi, 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.
Ankara has in the past been accused of turning a blind eye to the rise of IS 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 IS just 14 hours after it was launched.
Television footage showed the Syrian fighters walking into an apparently deserted and abandoned Jarabulus unchallenged.
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 President Recep Tayyip Erdogan staged by rogue elements in the armed forces.