Soldiers of the Free Syrian Army, defectors from the regular armed forces, attacked an air force intelligence base near the capital Damascus, activists said.
"The Free Army struck with rockets and RPGs (rocket-propelled grenades) the headquarters of air force intelligence which is located at the entrance of Damascus," the Local Coordination Committees, an activist network, said in a statement, adding smoke was rising from the area.
Activists, who illustrated the three-pronged attack in a plan attached to their statement, said prisoners being detained at the intelligence branch "were well" but the operation failed to secure their release.
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The Khaled ibn Walid Brigade, which is part of the Syrian Free Army and active in the central city of Homs, welcomed the attack near the capital.
"We pay tribute to our brothers, the rebel heroes, and may God bless your hands for your dawn operation targeting the intelligence building in Harasta."
The Syrian Observatory for Human Rights confirmed the news in an email statement received by AFP in Nicosia.
Meanwhile, security forces ambushed and shot dead four people -- three defectors and one civilian -- in the rural town of Keferzita in Hama province the same source said.
"Explosions shook Zamalkeh, Hamuriya, Douma, Harasta and we have confirmed reports that the headquarters of the security services in Harasta was hit," the Britain-based watchdog said.
There was no immediate word on any casualties or the motives of the attack.
In the capital, the Observatory said "three explosions shook the neighbourhood of Barzeh" and that these were "followed by heavy gunfire that continues until now."
And in the southern province of Daraa, cradle of the eight-month revolt against President Bashar al-Assad, "heavy shooting could be heard in all districts of Jassim" during Tuesday night.
The attacks came as Arab foreign ministers gathered in Rabat to keep up the pressure on the Damascus authorities to honour the terms of an Arab League peace blueprint they signed up to on November 2.
Syria will not be represented at the meeting.
