The Free Syria Army has said UN observers were not the target of the bomb which exploded Wednesday near a Damascus hotel, wounding three.
AP reported that the blast was in the car park of a military car park, after a bomb was planted on a fuel lorry. UN staff use the Dama Rose hotel close to the site of the explosion.
The area is home to the Syrian army officers club and a building belonging to the ruling Ba'ath Party.
At least 21 explosions have been heard across Damascus in the hours after the explosion.
The FSA said it had targeted a meeting between army officers and members of the Shabiha, a pro-government militia.
None of the victims of the attack were members of the UN mission.
Deputy Foreign Minister Faisal Mekdad told state media: "This was a criminal act aimed at distorting Syria's image."
The UN's emergency co-ordinator Baroness Amos is currently in Damascus, saying earlier this week that the situation has "got worse since I was here in March.
"Our partners, the Syrian Arab Red Crescent have been doing and extremely good job trying to make sure the people who need help get help, we will continue to support them but also work to scale up our own efforts."