In its report, the U.N. panel of inquiry said the Syrian government used local militias for mass killings and was targeting civilian areas with missiles, The Guardian reported Monday in a blog.
The report also said it was investigating reports rebels fired mortars against civilian areas and still recruit child soldiers.
The panel also said both sides used medical care as a war tactic.
The Guardian also reported al-Qaida claimed responsibility for killing 48 Syrian soldiers and state employees in Iraq last week. The militants said the dead's presence was evidence of complicity between the Shiite-led government of Iraq and Syrian President Bashar Assad.
In a statement, the group's Iraqi affiliate said its supporters ambushed the troops in Anbar province.
Russia's Interfax news agency said a Ukrainian journalist threatened with execution by her rebel captors has escaped.
Dmytro Astafurov, journalist Anhar Kochneva's cousin, told Interfax she "escaped this morning [Monday]. We talked with her by phone for a couple of minutes. She said that people took her to Damascus."
A humanitarian worker just returned from Syria, where the civil war passed the 2-year mark, said thousands of Syrians have been forced to live in graves, catacombs, and caves to escape the shelling in Idlib province, The Guardian reported.
Michal Prezdlacki, head of the Syrian mission for the Czech charity People in Need, said such extreme behavior should move the international community to establish humanitarian corridors to some of the hardest hit areas.
The Guardian reported 20 more bodies of young men believed killed by Bashar's forces were found in the "river of martyrs," a waterway in Aleppo. The Guardian said it published an investigation into the killing of 100 people found in the waterway in January.