A convoy of pro-Syrian government fighters entered the Kurdish-held enclave of Afrin in Syria Tuesday before they were targeted by Turkish artillery fire in a dramatic escalation of the conflict in northern Syria.

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The convoy of pro-Syrian government fighters in pickup trucks mounted with heavy weapons entered Afrin, where Turkey has been conducting a month-long military operation.

Video clips posted on Twitter showed fighters in camouflage fatigues and waving Syrian flags crossing a checkpoint that bore the insignia of a Kurdish security force.

"One Syria, one Syria!" some of them chanted.

Large military convoy of Iran-backed Syrian NDF (Shabiha) units heading from Nuble and Zahra to Afrin to support YPG against TSK/FSA. pic.twitter.com/1G3zxy5huD Stork (@NorthernStork) February 20, 2018

But shortly after they entered the Kurdish-held enclave, the pro-Damascus forces came under Turkish artillery fire and turned back, said Turkish President Recep Tayyip Erdogan.

At a news conference in Ankara, Erdogan said the convoy was made up of “terrorists” acting independently.

"Unfortunately, these kind of terror organisations take wrong steps with the decisions they take. It is not possible for us to allow this. They will pay a heavy price," said Erdogan.

The Syrian Kurdish YPG (Kurdish Peoples’ Protection Unit) however denied Erdogan’s assertion that the convoy had turned back under Turkish artillery fire.

YPG officials hailed the arrival of the pro-government forces -- which included militias allied to Assad but not the Syrian army itself -- and said Damascus had heeded its call for help against Turkey.

The British-based monitoring group, the Syrian Observatory for Human Rights, said one convoy had entered Afrin while another turned back.

The pro-Assad forces, called the national defence force, is akin to Saudi Arabia’s national guard, according to Peter Ford, former British ambassador to Syria. “These are fully fledged, paid for by the Syrian government forces and they have carried out many battles, including battles against ISIS,” said Ford, referring to the Islamic State (IS) group.

According to Cédric Mas, a Marseille-based Syria analyst and historian, the national defence forces “are trying to save the situation, while the [Syrian] army is bleeding from desertions and losses during the early years of the conflict. These forces are raised and appointed thanks to Tehran, they follow Iran’s orders.”

On Monday, Syria’s official news agency SANA said “popular forces” backing Syrian President Bashar al-Assad would enter the Afrin enclave “within hours” to “bolster” local forces confronting Turkish “aggression”.

The claim was denied Monday afternoon by theYPG,underscoring the difficult negotiations between Kurdish forces and the Assad regime.

The latest confrontation pits the Turkish army and their allied rebels directly against the military alliance backing Assad, further scrambling the already messy battlefield in northern Syria.

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Earlier Tuesday, Turkish President Recep Tayyip Erdogan said Turkish forces would "swiftly" lay siege to the centre of the town of Afrin "in the coming days".

His remarks to parliament came as Turkey's operation "Olive Branch", a ground and air offensive against the YPG militia, which Ankara brands "terrorists", entered its second month.

Erdogan said he had previously reached an agreement with Russian President Vladimir Putin and Iran's President Hassan Rouhani, Assad's main international backers, to block Syrian government support for the YPG fighters.

Video: Former UK Ambassador to Syria Peter Ford

Turkey and Russia have supported opposite sides throughout the war, with Moscow the closest ally of Assad and Ankara one of the principal supporters of rebels fighting to overthrow him.

However, in recent months Turkey has lent support to a Russian-led effort to end the war with most population centres in the hands of Assad's government. Ankara said last month it sought Moscow's agreement before launching the Afrin assault.

But speaking to FRANCE 24, Peter Ford, former British ambassador to Syria, explained that while Russia would like to protect its important relationship with Turkey, “when push comes to shove, Russia will side with Syria. It’s noticeable that the Turks have not been able to use their air force in Afrin. Why? Because the Russians won’t let them. The Russians can determine who is allowed into Syrian airspace west of the Euphrates [River] and Afrin is west of the Euphrates", Ford explained.

Assad's other main ally, Iran, is more closely involved than Russia with the militias that back the Syrian government on the ground, such as those who entered Afrin on Tuesday.

The Turkish offensive has made gains along almost all the border area with Afrin, pushing several kilometres (miles) into Syria and seizing villages. But the YPG still holds most of the region including its main town, also called Afrin.

(FRANCE 24 with AP, AFP and REUTERS)

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