Turkish media reported Turkish forces struck areas around the pro-Assad volunteers group as they moved from the towns of Nubl and Zahraa to the YPG-controlled enclave.

Video footage published on social media purported to show members of the al-Baqir Brigade, a part of the pro-government National Defence Force, or NDF, travelling to the province:

The Baqir Brigade said on Facebook it would be leading pro-government forces "against FSA terrorists and Turks" in Afrin, in reference to rebels fighting on Turkey's behalf.

The move comes in spite of an apparent promise extracted from the Russian president, Vladimir Putin, by his Turkish counterpart Recep Tayyip Erdogan that there would not be any Syrian army presence in Afrin.

Speaking after a speech in parliament on Tuesday, Erdogan said: "The [Syrian deployment] was seriously stopped yesterday... It was stopped."

Erdogan on Monday had spoken to his Russian and Iranian counterparts, Putin and Hassan Rouhani, to discuss developments in Syria and Afrin.

"Yes, it was stopped after those talks,” Erdogan said.

A spokesman for the YPG said the Syrian government had responded to a request for support against the Turkish-backed forces.

"Syrian government responded to invitation and responded to call of duty and sent military units on Tuesday 20 February 2018, to focus on the border and participation in defence of unity of Syrian territory," said Nuri Mahmoud, in a statement.

The announcement of an imminent siege on Afrin's centre has heightened concerns of increased civilian casualties and deprivation to medical access and other basic needs.

The monitoring group Airwars said the toll of civilian casualties in Afrin as of 14 February stood at 63-99 deaths caused by Turkish fire in Afrin's vicinity and 14-32 deaths caused by the YPG in Afrin and also in attacks on Turkish soil.

Reporter’s code: 50101