United Nations (United States) (AFP) - UN Secretary-General Antonio Guterres on Saturday called for an end to fighting in northwestern Syria, where hundreds of combatants reportedly died this week as regime forces advanced on a rebel-held town.

Syria's Russian-backed forces are advancing on the rebel-held town of Saraqeb amid a double-pronged push into Idlib province, home to some three million people, half of whom have been displaced from other parts of the country.

"The Secretary-General is deeply concerned by the ongoing military escalation in northwest Syria and calls for an immediate cessation of hostilities," his spokesman said.

"He reaffirms that attacks on civilians and civilian infrastructure, including on healthcare and educational facilities, are unacceptable."

The fighting in Idlib and in western Aleppo over the past week has killed 205 pro-government fighters and 220 anti-regime combatants, the Syrian Observatory for Human Rights said.

UNICEF said Saturday that violence this week forced 6,500 children to flee daily, bringing the total number of displaced children in northwest Syria to more than 300,000 since early December.

The Idlib region is dominated by jihadists from the Hayat Tahrir al-Sham alliance, led by a former Al-Qaeda affiliate.

Damascus, which controls more than 70 percent of Syria, has repeatedly vowed to reclaim the entire country, including Idlib.