More than 20 civilians were killed in Syrian government attacks on targets, including schools, in a relentless advance on the northwestern province of Idlib, the final major territory in Syria still controlled by opposition fighters.

According to UK-based war monitor the Syrian Observatory for Human Rights, government aerial bombing killed at least nine children and three teachers in Idlib city on Tuesday.

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Another four people, including a mother and her two children, died in government shelling of the town of Binnish, northeast of Idlib city, the monitor said.

At least six children were among 10 civilians killed by a Russian air attack on a shelter for displaced families in Maarat Misrin, a town just north of Idlib city on the road to the Turkish border, said Yahya Jaber, a rescuer in the civil defence emergency response force.

8 schools and kindergartens were deliberately targeted today by the regime’s warplanes and rockets loaded with cluster bombs. 21 people were killed, including teachers. Are school children and teachers the threat the regime and Russia must rid #Syria of?! pic.twitter.com/8m6jdOTGlo — The White Helmets (@SyriaCivilDef) February 26, 2020

The Syrian Observatory reported government forces recaptured 19 towns and villages over a 48-hour period. Among them was Kafranbel, a symbolic town that was among the first to rebel against the rule of President Bashar al-Assad in 2011.

The Idlib region hosts about three million people in increasingly desperate circumstances. Many are civilians forced from their homes in earlier phases of the war that has killed hundreds of thousands of people and displaced more than 11 million.

Save the Children on Tuesday called for schools to be spared the onslaught.

"Schools must be safe havens for children, even in a conflict zone," the charity's Syria response director, Sonia Khush, said.

"Today's attacks are another sign that fighting in northwest Syria has reached catastrophic levels of violence against children and civilians ... Nowhere is safe, not even school."

War's worst emergency

With backing from Russia, al-Assad's government and allied forces have in recent weeks pressed a major offensive against the last bastion of opposition to his rule.

Amid the bitter winter cold, the military operation has displaced nearly one million people since December, where they sought shelter near the Turkish border.

Syrian and Russian attacks have repeatedly targeted schools and health facilities in the area, despite appeals from aid groups and world powers to respect international law.

In Geneva, the International Committee of the Red Cross (ICRC) called on the warring sides to allow safe passage for civilians to escape attacks. It reminded them that hospitals, markets and schools are protected by law.

"We are urging parties to allow civilians to move to safety, either in areas they control or across the front lines," ICRC spokeswoman Ruth Hetherington said.

Several countries as well as the United Nations have made urgent calls for a ceasefire in Idlib, where the current humanitarian emergency has been described as the worst since the start of the conflict.

"Vast numbers of families have been forced from their homes many times in search of some semblance of safety and stability," Khush said.

According to the UN's Office for the Coordination of Humanitarian Affairs, some 170,000 people are sleeping rough in Idlib, which saw snow and sub-zero temperatures earlier this month.

Russia, Turkey to talk

On Monday, Turkey-backed opposition fighters seized the town of Nairab, which lies close to a junction between two major highways.

Their next goal was the strategic town of Saraqeb where the M5 highway, Syria's main north-south artery linking Damascus and Aleppo, meets the road west to the Mediterranean.

Rebels said the capture of Nairab put the M5 road within range of their guns, just days after the government in Damascus declared it fully open to traffic for the first time in years.

"The capture of Nairab has restored opposition morale and the next target of the campaign is Saraqeb," said Syrian military defector general Ahmad Rahhal.

The fighting has strained ties between Turkey and Russia, which back opposing sides in Syria's conflict.

Russia earlier this month blocked a UN bid to end the Syrian government's assault on Idlib.

Moscow's Foreign Minister Sergey Lavrov said on Tuesday a truce at this stage would be tantamount to "capitulating before terrorists".

Turkish President Recep Tayyip Erdogan said there was not yet agreement on holding a March 5 summit he proposed with Russia, France and Germany on the Idlib conflict, but he may meet Russian President Vladimir Putin on that date. He said a Russian delegation will visit Turkey on Wednesday to discuss the situation on Idlib.

Turkey, which backs rebels fighting al-Assad's forces and its allies, said it will send reinforcements to Idlib as troops there were being surrounded.

"We are sending the military reinforcement to protect our already existing 12 military observation posts in the Idlib area," said Ibrahim Kalin, the presidential spokesperson. "Some of those military posts have been now surrounded by the regime forces, so we had to take action to protect our soldiers there and also the civilians."

"Civilian situation is really getting worse by the day and we are the only one trying to protect civilian people from the regime attacks."

Since Turkey poured troops into northwest Syria to halt the Syrian government forces' campaign, 17 members of the Turkish forces have been killed.