BEIRUT // Two suicide bombers, one driving an ambulance packed with explosives, blasted an air force intelligence base near Damascus, a jihadist group which claimed the attack and a watchdog said on Tuesday.
The attack last night in Harasta north-east of the Syrian capital sparked intense fighting between rebels and the army, which at daybreak pounded the town with shells, the Syrian Observatory for Human Rights said.
"We cannot confirm the exact number of casualties right now, but we expect the number is very high," Rami Abdel Rahman, the Observatory director, said.
The attack was claimed by the Al Nusra Front, which was unknown before the start of the revolt against the regime of President Bashar Al Assad but which now regularly issues statements claiming suicide attacks in Syria.
"In revenge for those who have oppressed or killed Muslims, the decision was taken to strike the Air Force intelligence branch in Harasta," Al Nusra said in a statement posted online.
The group described a three phase operation in which a suicide bomber drove a car loaded with nine tonnes of explosives to the front of the building, and 25 minutes later, another fighter drove through with an ambulance containing explosives.
The fighters then targeted the area with mortars, according to the statement.
The Observatory confirmed that an air force intelligence branch in Harasta was bombed last night, followed by a second blast that hit a nearby army maintenance centre about 20 minutes later.
It said that the bombings shook the adjacent Damascus neighbourhoods of Qaboon and Jobar.
State media made no immediate mention of the bombings.
Meanwhile, a Turkish news agency said additional fighter jets have been sent to reinforce an airbase in the south-east amid escalating tensions with Syria.
The Dogan agency quotes unidentified military sources saying that at least 25 additional F-16 fighter jets were deployed at Turkey's Diyarbakir airbase last night.
The Turkish military's chief of staff inspected troops along the border with Syria today.
Turkey and Syria have been firing artillery and mortars across their volatile border since last week after shelling from Syria killed five civilians.
The move is also seen as bolstering Turkish forces along the Iraqi border. Turkish jets struck Kurdish rebel targets in two separate cross-border raids in northern Iraq on Sunday despite warnings from Baghdad.