At least 23 civilians have been killed in air raids launched by Syrian government warplanes as part of an ongoing offensive to gain ground in Idlib province from opposition fighters, according to a war monitor.

The ongoing raids claimed 16 people's lives on Monday after targeting several towns in the province the night before, according to the UK-based Syrian Observatory for Human Rights (SOHR) and Syrian Civil Defence.

The shelling hit a local hospital that is now unable to provide services, SOHR reported.

The push has forced thousands of civilians to flee towards the border with Turkey in harsh winter conditions, according to humanitarian groups.

Idlib is supposed to be one of the so-called de-escalation zones set up in Syria last year with the backing of Russia, Iran and Turkey.

The plan's objective was to stop the fighting and offer safety to civilians in those four areas: Idlib province, East Ghouta, northern Homs province and the country's south, but the Syrian government and its allies have not abided by the deal and continue to target all areas included in the deal, apart from the south.

According to the United Nations, Idlib is home to an estimated 2.6 million Syrians, including many internally displaced people who have already fled fighting elsewhere in the country.

The attacks come as Russian-sponsored diplomatic talks over the future of Syria are set to begin in the Black Sea resort city of Sochi, but the main opposition bloc - the Syrian Negotiations Commission (SNC), also known as the Higher Negotiation Committee (HNC), has announced that it will boycott the conference.

On Saturday, at least eight people were killed in the besieged enclave of Eastern Ghouta, the last remaining rebel stronghold near the capital, Damascus. Government shelling violated a Russian-negotiated ceasefire, which had gone into effect hours earlier.

Eastern Ghouta has been under siege by the government since 2013, with some 400,000 residents suffering from acute food and medicine shortages.

The country has been locked in a vicious civil war since early 2011 when the government of President Bashar al-Assad cracked down on pro-democracy protests.

Since then, hundreds of thousands of people have been killed, and more than 10 million have been forced from their homes, according to the UN.