Suicide bombers targeted the main Syrian military headquarters in the heart of Damascus on Wednesday in the most significant attack in the capital in more than two months, triggering scenes of panic and widespread gunfire in which a reporter for an Iranian television channel was killed.

The early morning blasts at the Syrian army’s General Staff Command offered renewed confirmation that Syria’s rebels are capable of penetrating the upper echelons of the country’s military establishment. State television said the attack was carried out by suicide bombers, and it broadcast security-camera footage showing a white van exploding on the main highway just outside the headquarters’ perimeter fence. Moments later, there was a second explosion within the grounds that the anchor said was also caused by a suicide bomb.

Videos posted on YouTube showed clouds of dense black smoke billowing over the headquarters, located beside the city’s heavily guarded Umayyad Square, where numerous sensitive government institutions are based. Four guards were killed and 14 people were wounded, state media said.

The bombs were smaller than in some of the large-scale suicide attacks this year in which dozens of people died, but the attack still resonated across a city accustomed to explosions and gunfire because of its proximity to the military’s top command. It was the closest the rebels challenging the rule of President Bashar al-Assad have come to reaching his inner circle since a bombing in July killed four of his top security advisers, including the defense minister and Assad’s brother-in-law, Assef Shawkat.

Reports that the current defense minister and several military commanders were injured in this latest attack were “groundless,” Information Minister Omran al-Zoubi told state television, blaming the attack on “terrorists.”

The rebel Free Syrian Army’s Damascus Military Council and an Islamist group, Tajamo Ansar al-Islam, both asserted responsibility in statements on their Facebook pages. A Free Syrian Army spokesman, Col. Aref Hammoud, said the attack was a collaborative effort targeting security officials who he said had proved even more brutal than those killed in July.

“The number of Syrians killed doubled after they took over,” he said, speaking by telephone from southern Turkey.

The level of violence has soared since the beginning of summer, as the rebels gained in strength, the government escalated its crackdown and a U.N. peace mission in the country collapsed, bringing the number killed since the revolt erupted 18 months ago to nearly 30,000, according to activist groups.

Among dozens reportedly killed nationwide Wednesday were at least 40 residents of the Damascus suburb of Thiabiyeh, near the international airport, who were apparently shot dead execution-style by government forces, according to the Britain-based Syrian Observatory for Human Rights. Video posted on YouTube showed rows of corpses wrapped in blankets, all of them men of military age who had been shot in the head. Some reports said that the toll was far higher and that women and children were among those killed.

The bodies were discovered as panic spread in the wake of the bombings in Damascus. Residents said the blasts were followed by sustained gunfire lasting for at least two hours around the building and elsewhere across the city as wailing ambulances hurtled through the streets. Iran’s English-language Press TV later reported that its correspondent Maya Naser, a Syrian national, had been killed by a sniper’s bullet. The channel’s Damascus bureau chief, Hossein Morteza, who also runs the bureau of sister channel al-Alam, was injured, Press TV said on its Web site.

It was unclear, however, whether the gunfire was caused by panicked security forces firing into the air or clashes with rebels in the area. The Syrian Observatory for Human Rights said the shooting was apparently carried out by government forces “in order to open the roads for the ambulances and to prevent an approach to the area.”

The official Syrian Arab News Agency, however, blamed “random fire by some terrorists.”

“The authorities confronted the terrorists and pursued them in the surrounding area,” the agency said.

A woman who was traveling on a bus to work near the scene of the blasts said commuters fled for cover in a nearby park as ambulances converged on the area and gunfire erupted. “I was scared,” she said, speaking on the condition of anonymity because people who communicate with foreign media face imprisonment by the government. “They were scared. Everyone was grabbing their phones and talking.”

Suzan Haidamous contributed to this report.