Syrian state TV reports three people wounded in bomb blast near UN observer mission in Syrian capital.

DAMASCUS - A massive bomb blast on Wednesday rocked the heart of Damascus near the hotel used by the UN observer mission in Syria, in an attack claimed by the rebel Free Syrian Army.

The blast, which tore a huge hole out of a petrol tanker near the Dama Rose hotel, wounded at least five people, a military source at the scene said, while Syria's deputy foreign minister said UN staff were unscathed.

"The FSA operation targeted a military command office with explosives designed to go off at a meeting of army officers and members of the shabiha (pro-government militia) which decides on daily operations in Damascus," Maher Nuwaimi, head of the FSA coordination command in Syria, said.

Damascus has been hit by several bomb blasts, including an attack last month at the national security headquarters that killed three of President Bashar al-Assad's top security chiefs and was claimed by the FSA.

State television showed images of charred vehicles and the fuel truck, its rear end blown off and still smouldering from the blast as firefighters doused the area and security forces set up a cordon.

"Our primary goal is to secure the observer mission team and thank God no one from this mission has been hurt since it arrived in Syria," Deputy Foreign Minister Faisal Mekdad told reporters.

"We will confirm to the United Nations that we will make every possible effort to secure their protection so they may exercise their role properly," he said, adding that he had visited the observers and that they were all okay.

The UN Supervision Mission in Syria, which uses the Dama Rose as its headquarters, was not immediately available for comment. UNSMIS chief General Babacar Gaye had staged a press conference at the hotel on Monday.

The UN Security Council is due to meet on Thursday to discuss the future of the observer mission, whose mandate expires on August 19.

The tanker was in car park near the Dama Rose and a row of UN vehicles were seen parked nearby, untouched by the blast.

Elsewhere in the capital, security forces stormed at least two districts in the hunt for rebels, in one area using tanks and army vehicles, according to activists.

It is the third straight day security forces have swept central areas of the capital, according to the Britain-based Syrian Observatory for Human Rights.

The Local Coordination Committees, a network of activists on the ground, also reported shelling in the Midan district of central Damascus.

In Syria's second city Aleppo, the army pounded the battleground districts of Saif al-Dawla, Sukari and Salaheddin in the south as well as the eastern rebel-held districts of Sakhur and Tariq al-Bab.

The army began its advance on Saif al-Dawla on Monday after last week retaking the neighbouring southwest district of Salaheddin, which still however has pockets of rebel fighters.

The northern metropolis is seen as pivotal to the outcome of the conflict, with some referring to it as Syria's Benghazi, the Libyan city that was the cradle of the revolt that toppled Moamer Kadhafi's regime.

Elsewhere in Aleppo province, one civilian was killed, while 10 civilians, including a child and four women died in shelling in the northwest province of Idlib, the Observatory said.

The violence followed a day in which 151 people were killed across the country -- 63 civilians, 39 rebels and 49 soldiers -- said the watchdog.

According to Observatory figures, over 23,000 people have been killed in Syria since the start of the anti-regime revolt, now entering its 18th month.

This figure is impossible to verify and the United Nations has stopped maintaining an independent toll.