ON THURSDAY morning al-Qazzaz, a southern suburb of the Syrian capital, Damascus, was shaken by two explosions. The twin bombs exploded at rush hour, damaging the building of one of the most feared of Syria's 17-odd security agencies, leaving craters in the street and turning cars in twisted metal cages.

The bombs seem planned to inflict the maximum casualties possible. The first explosion, a small one in the early morning rush hour, drew a crowd of people. It was followed by a second massive blast that reverberated across the city. State television, though not the most reliable source, said that at least 55 people were killed and almost 400 injured. Witnesses at the scene describe bodies scattered amid the destruction. These are not the first explosions to hit Damascus—in fact bombs have become a regular occurrence—but the second blast today was the biggest yet. Many security buildings in the centre of the capital are already cordoned off and protected by concrete barriers and sandbags.

It is impossible to know who is behind the explosions. Opposition figures and many Syrians believe them to be the work of the government, pointing out how quickly state television's cameramen were at the scene. The Syrian government blames "terrorists", a byword for the opposition. Others, who say that few have the expertise to denote explosions this large, point to jihadi groups. Jabhat al-Nusra (the Salvation Front), a group which has claimed responsiblity for previous bombings in recent months, is one possibility.

The UN now has 70 observers in Syria but their work has been hampered by the deteriorating security situation. Security forces are increasingly turning their attention to peaceful activists in the capital as well as attacking smaller villages and towns that off the UN monitors' radar. Worryingly for Syrians looking to outsiders for help, the latest attacks could prompt the few remaining European embassies in the capital to rethink their presence.