Two explosions have hit the Syrian capital, Damascus, with state TV saying dozens have been killed or wounded in "terrorist bombings".
State TV footage of the blasts showed massive destruction in the al-Qazzaz suburb to the south of Damascus.
Damascus has been the target of several bombs in past months amid continuing anti-government unrest.
The area has been cordoned off, but large crowds have gathered.
The first blast was apparently to attract people to the scene and was quickly followed by a second, much bigger explosion, a local journalist who spoke to eyewitnesses told the BBC.
Television footage showed dozens of mangled and burnt vehicles, some containing bodies. A large crater could be seen in the road.
The district is said to house a military intelligence complex, including the headquarters of the counter-terrorism operation for the military security in Syria, involved in President Bashar al-Assad's crackdown on pro-democracy protests.
Next to it was another military security intelligence building which was also destroyed in the attack.
The first blast occurred just seconds after UN staff had passed by. The observers are in Syria as part of the joint UN-Arab League peace plan.
There are now about 70 monitors in Syria but their presence has had no effect in quelling the violence.
Deraa was where the uprising against the government of President Bashar al-Assad began in March 2011.