'Around 35 tanks and other heavy weapons, carried aboard tank carriers, crossed the Jarablos border crossing in the early evening,' Rami Abdel Rahman, the head of the Britain-based Syrian Observatory for Human Rights, told AFP
Turkey on Saturday sent military reinforcements to northern Syria near an area controlled by Kurdish forces as Ankara threatens to carry out a fresh offensive to wipe them out, a war monitor said.
The move comes after US President Donald Trump's surprise announcement on Wednesday of the withdrawal of American troops stationed in north eastern Syria alongside Kurdish fighters, a long-time enemy of Turkey.
Washington has for years supported the Kurdish-led Syrian Democratic Forces (SDF) in the fight against the Islamic State group in Syria, as part of an international anti-jihadist coalition dominated by the People's Protection Units (YPG).
But on Wednesday Trump said he was ordering a withdrawal of the estimated 2,000 US troops in Syria because IS had been defeated, an assessment rubbished by many.
"Around 35 tanks and other heavy weapons, carried aboard tank carriers, crossed the Jarablos border crossing in the early evening," Rami Abdel Rahman, the head of the Britain-based Syrian Observatory for Human Rights, told AFP.
"They headed for an area near the Sajour River, between Jarablos and Minbej, not far from the front lines where Kurdish fighters of the Minbej Military Council are stationed," he added.
Turkey accuses the YPG of being a "terrorist offshoot" of the outlawed Kurdistan Workers' Party (PKK) which has been waging an insurgency against the Turkish state since 1984.
Turkish President Recep Tayyip Erdogan on Friday vowed to drive both the YPG and IS from Syria.
Ankara fears a Kurdish state could be established on its borders, which it believes could reinforce separatist ambitions of the Kurdish minority in Turkey.
The Kurdish community accounts for 15% of Syria's population and controls around 30% of the country, as a federal region declared in 2016.
In the past two years Turkey has conducted two offensives into northern Syria. In 2016 it launched an operation against IS, which also aimed to block the YPG from joining up the territory it held in northern Syria.
And in January 2018 Turkey staged an offensive against the militia in its north western enclave of Afrin.