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Mohammed Shaar, the Syrian interior minister, also blamed a suicide bomber for "detonating himself with the aim of killing the largest number of people".
The blast came exactly two weeks after twin bombings killed 44 people in the city.
"The opposition, on the other hand, is saying that this is a plot staged by the government to deter thousands of people that were planning to converge on that same spot to call for the international community to step in and enforce a no-fly zone and enforce also a dramatic of the regime in Syria."
Colonel Riad al-Asaad, the head of the Free Syrian Army, has dismissed the government's report of the attack, saying that Friday's explosion was "the work of the regime, just like the previous two explosions."
The head of the Arab League said on Friday he had asked the Damascus-based leader of the Palestinian group Hamas to ask the Syrian government to work to halt violence in the country.
Nabil Elaraby, the Arab League secretary-general, was speaking alongside Khaled Meshaal after a meeting in Cairo.
Last month's bombings targeted security buildings in the capital and were also the work of suicide bombers, the Syrian authorities have said.
Syria has been racked for 10 months by an uprising against President al-Assad in which the UN says more than 5,000 people have been killed.
The government says armed "terrorists" have killed 2,000 members of the security forces.