(Corrects 4th paragraph to say a general, not interior minister, killed in July 18 attack)
By Samia Nakhoul and Oliver Holmes
BEIRUT, Sept 26 (Reuters) - Syrian rebels bombed a military complex in Damascus on Wednesday, striking at the heart of President Bashar al-Assad's power and igniting a fire which gutted the army command headquarters.
The Free Syrian Army, the main rebel force fighting to overthow Assad, claimed responsibility for the attack which it said killed dozens of people.
But an armed forces statement said military leaders were unhurt and only a number of guards were wounded in the blasts, which shook the whole city at around 7 a.m. (0400 GMT) before regular working hours.
It was the biggest attack in Damascus since July 18 when a blast killed several senior security officials, including Assad's brother-in-law, the defence minister and a general.
That attack paved the way for a rebel advance into the centre of the capital, although they have since been pushed back to the outskirts.
Internet footage of Wednesday's fire at the General Staff Command Building in central Umayad Square showed flames engulfing its upper floors, indicating explosives were planted inside the building itself.
The main gate was completely blackened from the fire while all the windows of the building were blown out. Shards of glass littered the nearby streets, Reuters television foootage showed.
The blast gouged a deep crater, apparently where the explosive-laden car blew up.
Residents reported that gunfire rattled out around the district for at least two hours after the explosions. Roads in the area were blocked off as ambulances rushed to the scene.
"All our colleagues in the military leadership, the army staff command and the Defence Ministry are unhurt," Information Minister Omran Zoabi told Syrian Television.
Security forces were chasing "armed terrorists" - a term the authorities use to refer to insurgents waging war to oust Assad.
"It's a terrorist act, close to an important site, that's true. But as usual they failed to achieve their goal," he said.
Activist Sami al-Shami said the main explosions were caused by a suicide car bombing and second car loaded with explosives on the perimeter of the complex.
"Then the fighters went inside and clashed with security inside, while some of the men started to torch the building".
"There must be several security forces dead, there's no way the rebels could have made it in that far, fighting their way in, without killing any security forces," he told Reuters.
That appeared to tally with accounts from residents who heard gunfire and smaller blasts after the first explosions.
"The explosions were very loud. They shook the whole city and the windows of our house were shuddering," one resident reached by telephone said. "Black smoke was rising from the area near the army staff building."
A reporter for al-Manar television, run by Assad's Lebanese ally Hezbollah, said he was in the building after the explosion and saw the bodies of three "armed men", suggesting clashes between security forces and rebels at the site.
Another resident said: "I was woken up at four minutes to seven by the first loud explosion. Five or six minutes later there was a second."
"We're used to the sound of artillery but these were very big - bigger than usual. I can hear gunfire still," he said.
He said he saw soldiers on the roof of the nearby Air Force Intelligence building, part of the same military complex which was hit.
Syria's conflict, once a peaceful protest movement, has evolved into a civil war that the U.N. special envoy to Syria, Lakhdar Brahimi, said was "extremely bad and getting worse."
Activists say more than 27,000 people have been killed in the 18-month-old uprising against Assad, and even Damascus has become a battleground.
Pro-Assad gunmen killed at least 16 people in the city on Wednesday, the Syrian Observatory for Human Rights said.
The British-based Observatory said three of those killed in the poor district of Barzeh, which is sympathetic to opposition fighters, were children and six were women.
A correspondent for Iran's English-language Press TV was shot dead by a rebel sniper and its Damascus bureau chief was wounded while they covered Wednesday's explosions, Press TV said.
With no foreseeable prospect of foreign intervention and diplomacy stuck, outgunned rebels have relied increasingly on attacks with homemade bombs, striving to level the playing field against an army using fighter jets, artillery and tanks.
At the annual U.N. General Assembly in New York, French President Francois Hollande sought to shake up international inertia over the crisis by calling for U.N. protection of rebel-held areas.
"The Syrian regime ... has no future among us," Hollande said in a speech. "Without any delay, I call upon the United Nations to provide immediately to the Syrian people all the support it asks of us and to protect liberated zones."
Protection for "liberated" areas would require no-fly zones enforced by foreign aircraft, which could stop deadly air raids by Assad's forces on populated areas. But there is little chance of securing a Security Council mandate for such action given the opposition of veto-wielding members Russia and China.
The United States, European allies, Turkey and Gulf Arab states have sided with the Syrian opposition while Iran, Russia and China have backed Assad, whose family and minority Alawite sect have dominated the major Arab state for 42 years.
But Western powers have stopped short of supplying military aid to the rebels to an extent that could turn the tide of the conflict, in part out of fear of arming Islamist militants who have joined the anti-Assad revolt.
In another speech to the General Assembly, Qatari Emir Sheikh Hamad bin Khalifa al-Thani said Arab nations should intervene in Syria given the Security Council's failure to stop the civil war
Qatar, which backs the rebels, called on big powers to prepare a "Plan B" within weeks and set up a no-fly zone to provide a safe haven inside Syria in case mediator Brahimi fails to make headway.
The Qatari emir said he believed Arab and European countries would be ready to take part, despite their public wariness of committing the forces needed for such a mission.
Humanitarian conditions are worsening as the violence drags on. The president of the Syrian Arab Red Crescent, which has been the only relief group on the ground the entire 18 months of conflict, said it was in dire need of supplies.
"We need to concentrate mostly on health and shelter because there are 1.5 million displaced people," Abdul Rahman Attar told Reuters during a visit to Oslo. "We need more of everything." (Additional reporting by Dominic Evans and Erika Solomon in Beirut, Rania El gamal and Sami Aboudi in Dubai; Writing by Dominic Evans; Editing by Angus MacSwan)