At least 19 people, including 10 children, have been killed in a Syrian fighter jet strike on a school in the city of Aleppo, according to activists.
Bulldozers removed rubble from the smashed building, with children's drawings and paintings scattered in the debris, according to activist videos of the government air strike in the opposition-held eastern part of the city.
One of the drawings showed a hanging skeleton surrounded by skulls with a child nearby being shot by a gunman in a ditch. The child has a speech bubble written above her head in broken English that partly reads: "Syria will still free."
In another video by opposition activists, the bodies of 10 children wrapped in brown and blue sheets are seen on the floor of a hospital ward while a woman screams in the background.
The Britain-based Syrian Observatory for Human Rights, which covers the conflict through a network of activists on the ground, said at least 19 people were killed in the strike, including 10 children. The local Aleppo Media Centre put the toll at 25 killed, most of them children.
The United Nations Children's Fund said in a statement it was "outraged by the latest wave of indiscriminate attacks perpetrated against schools and other civilian targets across Syria".
Thousands of Syrian children have been killed in Syria's conflict, which began as an uprising against President Bashar Assad's rule, but has become a civil war that has killed more than 150,000 people and displaced millions.
Parts of the two-storey school appeared to have been completely smashed, according to the videos, which showed twisted metal and children's items, like a little red heart-shaped box.
Aleppo, Syria's largest city, has been divided between government forces and rebels for nearly two years, with constant fighting doing little to change the balance on the ground.
Forces loyal to Assad have been carrying out air strikes and dropping crude barrel bombs in rebel-held districts in the eastern part of the city, at times hitting schools, mosques and markets.
Rebels have hit back with mortar strikes and car bombs.
Mortar fire also killed three people near the central prison complex in Damascus, state news agency Sana said. A day earlier, a mortar strike in Damascus and a double car bombing in the central city of Homs killed at least 54 people.
In a statement, UN Secretary-General Ban Ki-moon condemned those attacks, calling them "horrendous acts of terror against innocent civilians".
At the United Nations, members of the Security Council said they fear that no progress will be made on getting desperately needed humanitarian aid into Syria as long as Russia opposes any actions against Assad's government.
Moscow has been a staunch ally of Damascus throughout the conflict. The US and its European and Gulf Arab allies are backing the opposition.
The UN estimates almost 3.5 million civilians inside Syria have virtually no humanitarian aid access. Millions of others suffer because of food and medicine shortages. Mr Ban has criticised both rebel and government forces for blocking efforts to get aid into the country.