Syrian government forces have taken control of several towns in northwestern Idlib province, a war monitor and Syrian state media reported, amid a renewed push by President Bashar al-Assad to recapture the last rebel stronghold.
Hundreds of thousands of people have fled Idlib in recent weeks amid stepped up air strikes by Russian and Syrian forces aimed at clearing the opposition from its last redoubt after almost nine years of civil war.
The Syrian Observatory, a war monitor, said on Sunday that six towns in the Idlib countryside had fallen to Syrian government forces in the past 24 hours.
The Observatory said the government advance, backed by heavy Russian airstrikes, has brought Assad's forces to the outskirts of Maarat al-Numan, a strategic urban centre about 33 km (20 miles) south of the city of Idlib on a highway that connects Damascus to Aleppo.
The push deeper into rebel-held territory has taken place despite a deal between Turkey and Russia, which back opposing sides in the conflict, for a January 12 cease-fire.
Turkish President Recep Tayyip Erdogan said on Friday that around 400,000 people from Idlib province were moving towards the Turkish border as a result of the surge in violence.
Turkey, which has a presence in the area and is seen by many civilians as a protector against Russian strikes, already hosts more than 3.5 million Syrian refugees and fears that millions more could cross the border.
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Moscow and Damascus say they are fighting jihadist militants that have stepped up attacks on civilians in Aleppo city in northern Syria, but rescue workers and rights groups say air strikes have hit civilian areas including hospitals and schools.
"The army's response will not be limited to the origins of attacks by armed terrorist organisations and will include devastating field operations that will not cease until the remnants of armed terrorism is uprooted," a military source was quoted as saying by state news agency SANA.