The Turkish army has intensified an offensive against Syrian Kurdish positions in the enclave of Afrin, as President Recep Tayyip Erdogan said there would be no "stepping back" in Ankara's operation, now in its third day.

Anadolu, Turkey's state-run news agency, reported on Monday that Turkish forces continued to shell Kurdish-held areas in northwestern Syria in support of Free Syrian Army (FSA) forces, who are on the ground in Afrin fighting alongside Turkish troops.

Al Jazeera's Stefanie Dekker, reporting from the Turkish-Syrian border near Afrin, said that "relentless, heavy shelling and artillery fire" could be heard kilometres away from the centre of the operation.

Turkish jets also hit targets at Afrin's Bursaya Mountain, which holds "strategic importance" for the Kurdish fighters, Anadolu said.

Turkey claims Kurdish forces are using Bursaya to target civilians in the Turkish province of Kilis.

Ground forces also advanced east of Afrin, in Syria's Azaz district, according to Anadolu.

Meanwhile, YPG fighters claimed they were able to repel the advance of Ankara-backed FSA forces and Turkish troops in four villages in two districts of Afrin.

Ankara says its "Olive Branch" operation is aimed at ousting the Kurdish People's Protection Units (YPG), which it brands as "terrorists", and create a so-called "safe zone" 30km deep to protect its border.

France has called for a UN Security Council meeting later on Monday to discuss developments in flashpoint areas in war-torn Syria, including the Turkish operation.

Earlier on Monday, Erdogan said the Turkish army was determined to press ahead with its push, saying that "there is no stepping back from Afrin".

Afrin residents told Al Jazeera's Dekker that while some women and children had fled to Aleppo, many others remained holed up in the city.

On Sunday, the YPG reported that six civilians and three fighters had been killed.

On the Turkish side, one person was reportedly killed and two others injured in the province of Hatay on Monday, following a cross-border YPG attack, according to Anadolu.

A soldier was also reportedly injured, but there were no reports of any Turkish military fatalities.

Meanwhile, the US-backed Syrian Democratic Forces (SDF) said on Monday it was studying the possibility of sending reinforcements to the Afrin region to fight the Turkish and FSA forces.

"We are in the framework of looking at the possibility of sending more military forces to Afrin," SDF spokesman Kino Gabriel told reporters, even as he urged Turkey to stop the operation.

The SDF is a multi-ethnic but predominantly Kurdish alliance of armed groups in Syria, and was a critical part in the fight against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group.

Turkey considers Syria's Kurdish Democratic Union Party (PYD) and its armed wing, the YPG, "terrorist groups" with ties to the banned Kurdistan Workers' Party (PKK), which has waged a decades-long fight inside Turkey.

Erdogan has previously said that all Kurdish armed groups "are all the same" and that changing their names "does not change the fact that they are terror organisations".