Turkey on Saturday launched operation "Olive Branch" seeking to oust from the Afrin region of northern Syria the Peoples' Protection Units (YPG) which Ankara considers a terror group, AFP reported.
Prime Minister Binali Yildirim said troops crossed into the YPG-controlled region in Syria at 0805 GMT.
Turkish artillery and war planes pounded YPG sites around Afrin and total of 153 targets, including YPG refuges and weapons stores have now been hit, according to the army.
The state-run Anadolu news agency said the Turkish troops, whose number was not specified, were advancing alongside forces from the pro-Ankara rebel Free Syrian Army (FSA) and were already five kilometers (three miles) inside Syria.
In his first comments on the offensive since it began, President Recep Tayyip Erdogan expressed hope the "operation will be finished in a very short time" and vowed "we will not take a step back".
Following calls from some Turkish pro-Kurdish politicians for people to take to the streets, he warned that anyone protesting in Turkey against the operation would pay "a heavy price".
The operation is Turkey's second major incursion into Syria during the seven-year war after the August 2016-March 2017 Euphrates Shield campaign in an area to the east of Afrin against both the YPG and Daesh.
The army said Daesh was also being targeted in this operation although it no longer has any major presence in the Afrin area.
Erdogan had repeatedly vowed that Turkey would root out the "nests of terror" in Syria of the YPG, which Ankara accuses of being the Syrian offshoot of the Kurdistan Workers' Party (PKK).
Afrin is an enclave of YPG control, cut off from the longer strip of northern Syria that the group controls to the east extending to the Iraqi border. Turkey wants the YPG to retreat east of the Euphrates River.
Yildirim was quoted as saying that the Turkish forces aimed to create a security zone some 30 kilometers (18 miles) deep inside Syria.
The Turkish military said it had hit 153 targets so far, including shelters and hideouts used by Kurdish militants. The YPG has said Turkey’s strikes killed seven civilians and three of its militants and wounded 13 civilians.
The YPG has also accused Turkey of striking civilian districts and a camp for the displaced in Afrin.
A YPG spokesman claimed that the Turkish forces had sought to enter Afrin "but we blocked the attack".
Intense Turkish artillery fire and strikes continued to hit some villages, the YPG said. Fierce battles raged to the north and west of Afrin against Turkish forces, said Birusk Hasaka, the YPG spokesman in Afrin.
In a sign of the risks to Turkey, four rockets fired by the YPG hit the border town of Kilis early Sunday, damaging one building and lightly wounding a woman.
Syrian President Bashar al-Assad slammed Turkey’s offensive as "support for terrorism".