The United Nations warned Friday of a new humanitarian catastrophe as an estimated 20,000 Syrians gathered along the border with Turkey amid escalating violence in the northwestern Syrian city of Aleppo.

One journalist posted images of the scene on Twitter.

The mass exodus comes as government forces launched a new offensive into the city, which is divided between rebels opposed to President Bashar al-Assad in the east and loyalist troops in the west.

Russian-backed Syrian regime forces made gains earlier on Friday, retaking Raytan north of the city and Atman in southern Daraa province.

No end to conflict in sight

Turkish PM Davutoglu warned that a crisis was brewing

The military push comes shortly after the government and its allies cut off the rebels' main supply route into the city.

Tens of thousands fled the city on Friday. Earlier, Turkish Prime Minister Ahmet Davutoglu warned that as many as 70,000 people could be heading toward his country's border.

The offensive occurred days after peace talks to end the conflict in Syria came to an abrupt halt in Geneva. Some Western leaders have blamed the Syrian government for the impasse, while others, including NATO head Jens Stoltenberg, have said the talks were undermined by continued Russian air strikes in the region.

A worsening crisis

Meanwhile, the United Nations said in its statement that access to affected people was becoming increasingly difficult amid the fighting.

On Thursday, government representatives in London pledged more than $10 billion (9 billion euros) to aid people displaced by the ongoing war, although leaders emphasized the need for a political solution to the conflict.

In addition to the 20,000 people gathered along the border, the UN says an additional 20,000 people have been displaced and are stranded in other parts of the country. More than half of the country's population has been displaced since the beginning of the conflict in 2011, and some 260,000 people have been killed.

blc/sms (AFP, dpa)