The UN Security Council was set to meet Thursday (February 6th) for an emergency session on Syria, as Syrian regime forces continued to press a Russia-backed offensive in the north-western province of Idlib.

The meeting was requested by the US, France and Britain, and UN envoy for Syria Geir Pedersen was expected to report on the situation in Idlib.

Turkey on Thursday urged Russia to press for an end to the Syrian offensive, which has undermined existing peace agreements and led to deadly clashes between Turkish and Syrian forces.

"We expect Russia to stop the regime as soon as possible," Foreign Minister Mevlut Cavusoglu said.

Turkish president Recep Tayyip Erdogan on Wednesday urged the Syrian regime to withdraw its troops from Turkey's military observation posts in Idlib.

Under a 2018 deal with Russia, Turkey has 12 observation posts in Idlib aimed at preventing a regime offensive.

The Morek and Surman posts are now encircled by the regime, and Turkish troops at another post in Saraqeb shelled regime forces on Wednesday to prevent it also being surrounded, the Syrian Observatory for Human Rights said.

Turkey has yet to comment on clashes at Saraqeb, but Cavusoglu said it would not allow "aggression" by Syrian regime forces.

US support for Turkey

The US on Wednesday offered help to Turkey and threatened sanctions to press the Syrian regime and Russia to halt the major new offensive.

James Jeffrey, the US point man on Syria, said the US was "very, very worried" about the "extremely dangerous conflict" that has flared up in the Idlib region.

"Certainly, we are moving forward on additional sanctions," Jeffrey said.

Though Tahrir al-Sham has consolidated its position as the main anti-regime faction on the ground, Jeffrey said he doubted Russia's justification that it had come under growing fire from the extremist alliance.

"We have seen only intermittent and not very strong or significant military actions on their part against the Russians," Jeffrey said.

"The Russians use this as an excuse, basically, to launch these massive attacks against the civilians," he said.

Jeffrey said the immediate solution should be a "permanent ceasefire" before talks on "all issues" including the status of the militants.

Regime forces enter Saraqeb

Syrian regime forces on Wednesday penetrated the strategic Idlib province town of Saraqeb, the Syrian Observatory for Human Rights said.

Observatory head Rami Abdel Rahman said regime forces had entered Saraqeb after hundreds of Tahrir al-Sham and allied fighters retreated north.

"Regime forces have begun to comb districts of Saraqeb and are on the point of taking control of all of the M5 road," he said.

The town sits on a junction of two key roads, the M4 and M5, which the regime is seeking to retake.

The M5 connects Damascus to Aleppo in the north, crossing Idlib, while the M4 connects Aleppo with the coastal city of Latakia.

A week ago, regime forces -- backed by Russia -- retook the town of Maaret al-Numan, which sits on the M5.

Calls for a humanitarian corridor

The EU on Thursday called for an end to the bombings in north-west Syria and the opening of a humanitarian corridor.

"Bombings and other attacks on civilians in north-west Syria must stop," the EU's diplomatic chief Josep Borrell said in a joint statement with the EU's humanitarian affairs commissioner Janez Lenarcic.

The top EU officials called for "unimpeded humanitarian access to people in need of assistance" as well as "respect of humanitarian law, including the protection of civilians".

Eight humanitarian aid organisations on Wednesday called for an immediate ceasefire in north-western Syria.

The aid groups -- including the Norwegian Refugee Council, Save the Children, Care and the International Rescue Committee -- labelled the situation a "humanitarian catastrophe".

The latest wave of more than half a million people fleeing follows 400,000 others who were displaced by an earlier round of fighting in Idlib last year.

Displaced 'running out of options'

Many have fled north towards the border with Turkey, where camps are overcrowded and thousands more have set up haphazard tents.

Jan Egeland, head of the Norwegian Refugee Council, warned that the newly arrived were running out of options as to where to go.

"Camps are hosting five times their intended occupancy and rental prices have skyrocketed in towns in the north-west," he said.

World Vision International head Andrew Morley said children were sleeping in flooded fields, and some families were even burning their clothes to stay warm.

"The exodus of people is staggering, and tens of thousands more are joining them every day," he said.

The recent violence has killed around 300 civilians, the Observatory said.

The World Health Organisation said Monday the violence had in January forced 53 medical facilities in north-west Syria to close and warned of "critical health threats" to fleeing civilians.