The Turkish foreign minister has said that Syrian forces cannot stop its army's advances in Afrin, in response to reports that the Syrian regime forces will fight alongside Kurdish YPG fighters in the border town.

Speaking at a press conference in the Jordanian capital, Amman, Mevlut Cavusoglu said on Monday that Turkey welcomed the entry of Syrian forces into Afrin if it was to confront fighters belonging to the Kurdish People's Protection Units (YPG).

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"If so, there is no problem. However, if they are entering [Afrin] to protect YPG/PKK, nobody can stop the Turkish army," he added, referring to the armed Syrian Kurdish group YPG, which controls Afrin, and banned Kurdistan Workers' Party (PKK) active in Turkey.

Ankara considers the Kurdish Democratic Union Party (PYD), active in Syria, and its armed wing YPG, to be "terrorist groups" with ties to the PKK, which has waged a bloody armed rebellion for decades in southeast Turkey.

The PKK has been designated a "terrorist" group by the United States, the European Union and Turkey.

"We have always expressed our support for Syria's territorial integrity ... We are one of the countries with the utmost support for it," Cavusoglu said.

The YPG fighters claimed earlier in the day that they had reached a deal to allow regime troops to enter Afrin in the northwestern part of the border town.

Assad forces to back YPG

Nuri Mahmoud, a spokesman for the YPG, told Al Jazeera earlier on Monday that they are calling on the Syrian government forces "to preserve a united Syria", in a development that could mean regime forces might directly confront Turkish troops in the region.

Turkey and the Free Syrian Army (FSA) - an Ankara-backed armed Syrian opposition group - launched an air and ground operation into Afrin last month to push the US-backed YPG fighters out and create a buffer zone on its southern border.

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"Syrian soldiers haven't yet arrived. We are calling on the Syrian army to protect Afrin, because we'd love to preserve a unified Syria," Mahmoud told Al Jazeera.

"We are saying this because the international community continues to address the Syrian leadership as sovereign and we call on this authority to protect its territory."

He added that Syrian government forces are expected to arrive within two days.

The PYD/YPG has come to control large swaths of northern Syria, including Afrin, in the course of the Syrian war as it led the US-backed Syrian Democratic Forces (SDF) umbrella organisation in the fight against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group.

US support for the SDF has infuriated Turkey and created the ongoing diplomatic crisis between the two NATO allies.

This latest development highlights the complex battlefield of northern Syria, which hosts a large number of actors, including the PYD/YPG, the Syrian government, rebel factions, Turkey, the US and Russia.

Syrian state news agency SANA also carried a report saying pro-government forces "will arrive in Afrin within a few hours to support its people's stand against the Turkish regime's attack on the area and its people".

A few hours after the SANA report, Turkish President Recep Tayyip Erdogan spoke on the phone with Russian President Vladimir Putin and discussed the "latest developments in Afrin", according to the Anadolu news agency.

They also discussed their efforts to set up new observation posts in Idlib in northern Syria, Anadolu said.

The posts are part of a joint Turkish, Russian and Iranian agreement to set up de-escalation zones in four areas in the region. Turkish forces have already established six observation posts in Idlib to monitor any fighting.