President Donald Trump has called for Russia to end its support for the Syrian regime's "atrocities" as he expressed US concern over violence in the Idlib region, the
White House said Sunday.
Turkey's foreign minister also pressed his Russian counterpart over the attacks by Damascus on the last rebel-held bastion in the country.
Backed by Russian air power, Syrian President Bashar al-Assad made fresh gains Sunday as he intensified his assault on the holdout northwestern province of Idlib.
Turkey has 12 observation posts in Idlib as part of a 2018 deal reached between Ankara and Moscow to prevent a regime offensive, but Syrian regime forces have pressed ahead regardless.
Four of the Turkish posts are believed to be encircled by Syrian forces, and Ankara has threatened to attack Damascus if they do not retreat by the end of February.
"I stressed that the attacks in Idlib must stop and it was necessary to establish a lasting ceasefire that would not be violated," Turkish Foreign Minister Mevlut Cavusoglu told journalists at the Munich Security Conference, after he met with Russian Foreign Minister Sergei Lavrov.
Rebel supporter Turkey and Damascus ally Russia have worked closely on Syria in recent years despite being on opposing sides of the nine-year conflict.
A Turkish delegation will head to Moscow on Monday, after Russian officials visited Ankara last weekend but failed to reach a concrete deal.
War monitor the Syrian Observatory for Human Rights on Sunday said regime forces "were in control of all the villages and small towns around Aleppo for the first time since 2012."
Regime forces have for weeks been making gains in northwestern Syria and chipping away at territory held by jihadists and allied rebels, focusing their latest operations on the west of Aleppo province.
The Russian-backed offensive has triggered the largest wave of displacement in Syria's civil war, with 800,000 people fleeing since it began in December, the United Nations has said.
Backed by Russia, Iran and the Lebanese Shiite movement Hezbollah, Assad's forces now control more than 70 percent of Syria and the president has repeatedly vowed to retake the entire country.
In the Saturday phone call with Erdogan, Trump also "reiterated that continued foreign interference in Libya would only serve to worsen the situation."
Libya has been mired in chaos since a 2011 NATO-backed uprising killed longtime dictator Moamer Kadhafi, with two rival administrations vying for power.
States including Russia, France, the United Arab Emirates, and Egypt support strongman Khalifa Haftar, while the UN-recognized Government of National Accord is backed by Turkey and Qatar.afp