The top U.N. humanitarian official Tuesday expressed concern about the deteriorating situation in the Syrian city of Aleppo, where hundreds of people have been killed or injured by indiscriminate attacks in recent weeks. "I join U.N. Secretary-General Ban Ki-moon in strongly condemning the attacks against civilians in Aleppo and in many other parts of Syria," Under-Secretary-General for Humanitarian Affairs Valerie Amos said. Ban last week voiced grave concern about the continued and indiscriminate use of heavy weapons and mortar shelling in the ongoing conflict, particularly in hard-hit Aleppo, which the government has targeted with "barrel bombs," or oil drums filled with explosives and shrapnel and dropped by aircraft. "People have suffered enough," Amos said, adding that insecurity continues to have a major impact on efforts to reach people with life-saving assistance. "I remind all parties to the conflict of their obligation under international humanitarian and human rights law, and their responsibility to ensure the protection of civilians."