An air strike by Syrian fighter jets hit a school in the northern city of Aleppo Wednesday, killing 18 people - many of them children.
Activists, including the Britain-based Syrian Observatory for Human Rights, say the air strike hit the Ain Jalout school in the Al-Ansari district of Aleppo. Videos posted by the activists show blood and debris and the bodies of at least 10 children on the floor.
The Observatory says at least 18 people died in the attack, while the Aleppo Media Center says 25 children were killed.
The United Nations Children's Fund said it is "outraged by the latest wave of indiscriminate attacks perpetrated against schools and other civilian targets across Syria."
Aleppo has been divided between government forces and rebels for nearly two years, with forces loyal to Syrian President Bashar al-Assad carrying out frequent airstrikes and dropping crude barrel bombs in rebel-held areas.
More than 150,000 people have been killed so far in fighting throughout the country.
Also Wednesday, members of the U.N. Security Council said they fear that little progress has been made on getting desperately needed humanitarian aid into Syria.
U.N. humanitarian chief Valerie Amos said a resolution passed in February aimed at eliminating obstacles to delivering aid is not working. She says less than 10 percent of the 242,000 people living in besieged areas have received assistance over the past four weeks.
"Far from getting better, the situation is getting worse. Violence has intensified over the past month, taking a horrific toll on ordinary Syrians."
Amos pointed out the Council had to pass a number of different resolutions under Chapter 7 of the U.N. charter to get the required humanitarian aid to people in crisis-hit areas in the past.
The U.N. says 3.5 million Syrians are living in areas that are under siege or where humanitarian assistance cannot reach them.