BEIRUT — Three suicide bombers detonated cars packed with explosives in a government-controlled area of the battleground Syrian city of Aleppo today, killing at least 33 people, leveling buildings and trapping survivors under the rubble, state TV said.

A fourth explosion a few hundred yards away struck near the edge of the Old City, a UNESCO World Heritage site that has been heavily damaged during more than two months of fierce fighting between rebels and government forces for control of the Aleppo.

There was no immediate claim of responsibility, but the government blamed its opponents and said the blasts were caused by suicide bombers. The technique is a signature style of al-Qaida-style jihadist groups, some of which are known to have entered Syria’s civil war to fight against the regime.