- NEW: Opposition member fears hundreds killed in bombings; the death toll is unclear
- "This is the largest blast I have ever felt since the uprising began," one man says
- Syrian state-run media have not reported any bombings near the air force compound
- Opposition: At least 31 people are reported dead across Syria on Tuesday
(CNN) -- Dual car bombs exploded near an air force intelligence compound outside Damascus overnight, an opposition group said Tuesday, though it's unclear how many people may have been killed.
"We fear that hundreds of regime forces have been killed in this attack because the compound hosts a large number of regime forces," said Rami Abdulrahman of the opposition Syrian Observatory for Human Rights. "We also fear for the lives of hundreds if not thousands of anti-government detainees that are being held in the basements of the air force security compound."
Syrian state-run news agencies have not reported any such blasts in Harasta, the Damascus suburb where the intelligence compound is located.
Tensions build in Syria 
Turkish shells rain on Syria 
Rebels attack army barracks in Damascus 
Turkey-Syria ties strained by violence But the blasts were among a barrage of explosions, gunfire and shelling reported from the Damascus area early Tuesday, suggesting the civil war may be zeroing in further on the Syrian capital.
"This is the largest blast I have ever felt since the uprising began," said Omar al Khani, an opposition activist. "One of my windows is blown out, and neighbors' plates were knocked down from the table to the ground."
Less than half an hour later, al Khani said there was another explosion, followed by intermittent gunfire as a thick plume of smoke unfurled across Damascus.
Violence in Harasta continued in the form of shelling, opposition activists said. At least one person was killed and several homes destroyed "due to the heavy and indiscriminate shelling" of the suburb, the Local Coordination Committees of Syria said.
And in the Damascus suburb of Daraya, at least 25 unidentified bodies were found burned, the LCC said. The group reported at least 31 people dead across the country Tuesday.
CNN is unable to independently confirm reports of casualties or violence because the Syrian government has restricted access by international journalists.
