At least four children were killed in Aleppo on Thursday when shells landed near their school, a monitoring group has said.

The British-based Syrian Observatory for Human Rights said the incident happened in al-Suleimaniya, a government-held area of western Aleppo.

According to the Syrian state news agency SANA, the school was targeted in a "terrorist" attack, the term the regime uses for all rebels.

The deaths come as the head of the Civil Defence rescue service in Aleppo, Ammar al Selmo, said 145 people had been killed in the rebel-held eastern part of the city on Tuesday and Wednesday.

Air strikes targeting rebel-held districts of Aleppo intensified on Tuesday, after a lull of several days which the Syrian army said was designed to allow civilians to leave.

The city has been divided between government and rebel control for years. "The bombing has been very intense," Selmo told Reuters on Thursday.

The Syrian army launched an assault to take rebel-held areas of Aleppo last month with Russian air support and Iranian-backed militias.

The UN estimates that 275,000 people are currently trapped in the east of the city. Hundreds have died since the beginning of last month's offensive, including more than 60 children.

Last week, the Archbishop of Canterbury, Justin Welby, said the bombardment of Aleppo was "demonic" and shows "absolute contempt for the human spirit".

In an interview with ITV News, Welby said: "What is being done is evil, it is demonic, it is the absolute contempt for the human spirit, for the dignity of the human being. It is the brushing aside of the poor and the weak and the fragile, in a way that is as bad as anything we've seen in the last century."

The Archbishop also called for Syria's President Bashar al-Assad to stand down, saying that to do so would be "heroic".

The US and other Western countries say Moscow and Damascus are guilty of war crimes for deliberately targeting civilians, hospitals and aid deliveries to crush the will of the people trapped under siege. The Syrian and Russian governments claim they target only militants.

Additional reporting by Reuters.