DAMASCUS/Beirut - At least 12 children and three adults were killed in a Russian air strike that hit a school in Syria's Aleppo province on Monday, a monitor said.

The Syrian Observatory for Human Rights said the three adults included a teacher, and that the strike in the town of Anjara also injured at least 20 people, all of them children and teachers. The monitor said there had been heavy air strikes and clashes between government and rebel forces since Sunday in the northern province, which is controlled by a mixture of moderate and Islamist rebels.

Photos distributed by media activists in Aleppo province showed a classroom full of rubble with the wooden tops of desks blown off their metal frames. The Britain-based Observatory also reported that three children were killed by rebel rocket fire on a government-held district in Aleppo city.

Control of the city has been divided between government forces in the west and rebel fighters in the east since shortly after fighting began there in mid-2012. Government forces regularly carry out air raids on the east, while rebels fire rockets into the west.

The situation is largely reversed in the countryside surrounding the city, with rebels controlling much of the area west of Aleppo, and the government present to the east. Russia, a staunch ally of President Bashar al-Assad's regime, began air strikes in support of the central government in late September.

It says it is targeting the Islamic State group and other ‘terrorists,’ but a third of those killed in its strikes have been civilians, according to the Observatory. The monitor said in late December that Russian air strikes had killed more than 2,300 people since they began on September 30, among them 792 civilians.

Moscow has slammed as ‘absurd’ allegations that its strikes have killed civilians. More than 260,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests. Moreover, dozens of aid trucks headed on Monday to the besieged rebel-held Syrian town of Madaya, where more than two dozen people are reported to have starved to death. The aid convoys were set to arrive in the town after an outpouring of international concern and condemnation over the dire conditions in Madaya, where some 42,000 people are living under a government siege.

The delivery will happen simultaneously with aid entering two government-held towns under rebel siege in the northwest of the country. It comes after the Doctors Without Borders (MSF) charity said some 28 people had died of starvation in Madaya since December 1.

Residents have described desperate scenes, saying they have been reduced to eating weeds and paying exorbitant prices for what little food could be smuggled through the siege. Forty-four trucks operated by the International Committee of the Red Cross, the Syrian Red Crescent, the United Nations and World Food Programme left from Damascus for Madaya on Monday afternoon.

Earlier, 21 trucks carrying similar supplies left for the government-held towns of Fuaa and Kafraya, which are under rebel siege in the northwest of the country. Fuaa and Kafraya are more than 300 kilometres (180 miles) from Damascus, while Madaya is about 40 kilometres from the capital.

The trucks are carrying food, water, infant formula, blankets and medication for acute and chronic illnesses, as well as surgical supplies. The three towns, along with rebel-held Zabadani next to Madaya, were part of a landmark six-month deal reached in September for an end to hostilities in those areas in exchange for humanitarian assistance.

A first aid delivery went ahead, and in December some 450 fighters and civilians from Zabadani, Fuaa and Kafraya were evacuated. But aid has not entered Madaya since October, and residents and rights groups have raised the alarm about deteriorating conditions inside.

Government forces have been able to airdrop some supplies into Fuaa and Kafraya, which are home to around 20,000 people, but rebel forces are not able to do the same for Madaya. Over the weekend, MSF said 23 people had died of starvation since December 1 at one of the facilities it supports in Madaya. On Sunday it reported five additional deaths, including that of a nine-year-old boy.

‘MSF-supported medics in the besieged town have 10 critical starvation patients needing urgent hospitalisation,’ the group said. It said that ‘200 more malnourished patients could become critical and in need of hospitalisation within a week if aid doesn't arrive.’

Another 13 people who tried to escape in search of food have been killed when they stepped on landmines laid by regime forces or were shot by snipers, according to the Syrian Observatory for Human Rights, a British-based monitoring group. The UN and aid agencies have regularly raised concern about besieged and so-called ‘hard-to-reach’ areas in Syria.

Last week, the UN said only 10 percent of its requested aid deliveries to hard-to-reach and besieged areas of Syria last year were approved and carried out. More than 260,000 people have been killed in Syria since the conflict began in March 2011 with anti-government demonstrations.

Elsewhere in Syria, the Observatory said at least eight children were killed along with their teacher when a Russian air strike hit their school in the west of Aleppo province. The strike injured another 20 students and teachers, the monitor said. Russia, a staunch ally of President Bashar al-Assad, began a campaign of air strikes in support of the regime in late September. It says it is targeting the Islamic State group and other ‘terrorists’ and has dismissed reports that its raids have killed hundreds of civilians as ‘absurd’.

Also in Aleppo, the Observatory said three children had been killed in rebel rocket fire on a government-held neighbourhood in Aleppo city. The city has been divided between government control in the west and rebel control in the east since shortly after fighting there began in mid-2012.