BEIRUT, Aug 17 (Reuters) - The Syrian air force bombarded an area northeast of Damascus on Monday, keeping up its attack on a rebel-held district where close to 100 people were killed on Sunday in an air strike on a market, the Syrian Observatory for Human Rights said.

Sunday's air strike on Douma, 10 miles (15 km) northeast of Damascus, was one of the bloodiest attacks of its type in the four-year-long war that has killed an estimated quarter of a million people and driven 10 million from their homes.

The Syrian opposition group, the National Coalition for Syrian Revolutionary and Opposition Forces, said the attack aimed to inflict as many civilian casualties as possible. The dead included children.

"Any talk of political and peaceful solutions in the shadow of massacres and excusing the criminal from punishment will have no meaning in realizing stability in Syria," Khaled Khoja, president of the Turkey-based coalition, said.