Hayat Tahrir Al-Sham (HTS), formerly known as Jabhat al-Nusra, the Syrian branch of Al-Qaeda terrorist group, chief Abu Mohammad Al-Jolani came out on Monday in a video addressing the ongoing talks between Syria and Turkey under the auspices of Russia, expressing his concern about the talks and underlining that they marked a "serious setback."

HTS "is facing a brand new challenge... and the talks between the Syrian regime and its Russian ally with the Turkish side constitute a serious deviation from our goals," al-Jolani stressed.

The international terrorist, whose group was founded on support from Turkey, called on the armed groups in northern Syria to form a united front with the HTS to "confront the existing threat."

Al-Jolani, talking in a concerned manner about Turkey's U-turn on him, the HTS chief warned his supporters of getting let down by their close ones, as well as their opponents, highlighting that "we have prepared ourselves for the great days to come," calling on them to stand by him and confront the upcoming challenges.

This comes after the Russian, Syrian, and Turkish defense ministers held talks on Wednesday in the Russian capital, Moscow, to discuss means of resolving the Syrian crisis, the former's defense ministry said.

"On December 28, trilateral talks between the defense ministers of Russia, Syria, and Turkey took place in Moscow. The meeting discussed ways to address the Syrian crisis, the issue of refugees, and joint efforts to combat extremist groups in Syria," the Russian Defense Ministry said.

At the conclusion of the meeting, the defense ministers highlighted how the dialogue was constructive, stressing the need for all three parties to hold further talks to bring more stability to Syria and the whole region, the statement added.

The meeting between the Syrian, Turkish, and Russian defense ministers in Moscow was positive, the Syrian Defense Ministry commented on the meeting.

"Today in the capital of Russia, Moscow, with the participation of the Russian side, a meeting was held between the Syrian defense minister and the head of the Syrian General Directorate with the Turkish defense minister and the head of Turkish intelligence," Damascus underlined.

Meanwhile, the Turkish Defense Ministry said Defense Minister Akar and the head of the Turkish National Intelligence Organisation (MIT), Hakan Fidan, met Syrian Defense Minister Ali Mahmoud Abbas and Syrian intelligence chief Ali Mamlouk in Moscow along with Russian Defense Minister Sergei Shoigu.

"Ways of resolving the Syrian crisis and the problem of refugees as well as joint efforts to combat extremist groups in Syria have been discussed," the Russian RIA Novosti news agency said, citing the Russian defense ministry.

Additionally, Turkish Defense Minister Hulusi Akar said on Christmas his country was in talks with Russia to use Syria's airspace to conduct a cross-border operation against the US-backed Kurdish YPG militia in northeastern Syria.

The United States has been arming Kurdish groups in northeastern Syria, making grounds for oil and gas theft.

Turkey has conducted a number of operations in northern Syria against the US-backed SDF and the YPG, threatening further incursions over a period of months. 

Earlier in December, Erdogan and his Russian counterpart Vladimir Putin held a phone call, during which they discussed several issues, such as bilateral ties and the Kurdish forces in Northern Syria.

Russia has been receiving indications from Ankara and Damascus about being open to making steps towards one another and about hopes for a Syrian-Turkish rapprochement, Russia's special presidential envoy for Syria, Alexander Lavrentyev, told reporters on November 23, following the 19th round of the Astana talks on Syria.

Erdogan has been threatening to conduct a new military incursion into northern Syria, with the Turkish President also saying that his country was committed to destroying the Kurdistan Workers' Party (PKK) "until its last militant is neutralized" and raised the possibility of conducting a ground operation soon.