Syrian state television is reporting that four security guards have been killed in two explosions near the Damascus general headquarters of Syria's army.
Wednesday's attack engulfed at least two floors of the building in flames and left 14 people injured.
Omran al-Zoubi, information minister, said the improvised explosive devices, one of which may have been placed inside the headquarters building itself, exploded minutes before 7am on Wednesday, shattering the windows of nearby buildings in the heavily guarded Umayyad Square district.
Rebel spokesmen for the Free Syrian Army released a statement claiming responsibility and saying that dozens had been killed, but Zoubi said the bombings caused "only material damage".
"I would like to assure everyone that all our military comrades at the ministry of defence and the army general staff are well and unharmed," he said.
"Security forces [are] chasing armed terrorists in the area … everything is normal … the news is false. Yes, it’s a terrorist act near an important location building, but they failed to achieve their goal."
A military source quoted by state television said that the attack involved one car bomb and one improvised explosive device. They denied any casualties among the army leadership.
Many roads in the centre of Damascus were blocked, and ambulances rushed to the scene, residents said.
They reported hours of gunfire following the incident.
The Syrian Observatory for Human Rights, the UK-based activist organisation, said that fighting erupted inside the general command compound after the explosions.
"I was woken up at four minutes to seven by the first loud explosion. Five or six minutes later there was a second," one resident told the Reuters news agency.
"We're used to the sound of artillery but these were very big - bigger than usual. I can hear gunfire still."
Al Jazeera's Rula Amin, reporting from neighbouring Lebanon, said even if senior military officials were not harmed "it is still an achievement for the rebels to come so close" to such an important strategic location in the Syrian capital.
The area is also near Syrian television and only kilometres from the residence of Bashar al-Assad, the Syrian president.
Our correspondent said the opposition fighters also referred to aid from people within the ranks of the army who have yet to officially defect, but who "in their hearts are with the rebels".
Call for Arab intervention
The attacks came the morning after Qatari Emir Sheikh Hamad bin Khalifa Al Thani for the first time called for unilateral Arab intervention in Syria.
Sheikh Hamad, speaking at the annual UN General Assembly in New York City on Tuesday, said Arab states must act out of "national, humanitarian, political and military duties" in the face of the UN Security Council's failure "to reach an effective position".
"In view of this, I think that it is better for the Arab countries themselves to interfere out of their national, humanitarian, political and military duties and do what is necessary to stop the bloodshed in Syria," he said.
Western powers are opposed to direct intervention, and the Security Council, which includes Syrian allies China and Russia, has been unable to pass even a resolution calling for President Bashar al-Assad to step down.
"We had a similar precedent when Arab forces intervened in Lebanon in the mid-'70s ... to stop internal fighting there in a
step that proved to be effective and useful," Sheikh Hamad said.
He urged countries to provide "all sorts of support" to Syrians until they gain legitimate rights.
US President Barack Obama, also speaking at the General Assembly on Tuesday, again called for the Assad's removal but provided no clear plan.
Arming of rebels denied
Qatar, along with Saudi Arabia and Turkey, strongly supports the mainly Sunni Muslim Syrian rebels, while mainly Shia Iran backs Assad, whose Alawite minority is an offshoot of Shia Islam.
Activists and the UN say that more than 20,000 people have been killed in Syria's uprising, which began as peaceful demonstrations for reform 18 months ago but turned into an armed campaign fighting to topple President Bashar al-Assad, with sectarian overtones that could drag in regional powers.
Media reports have suggested that rebels are purchasing some of their arms from sources in Turkey with funds provided by Qatar and Saudi Arabia, possibly assisted by US and European intelligence agencies.
Sheikh Hamad denied that Qatar had been arming the rebels, saying that his country provided logistic and humanitarian help, and said a Sunni-Shia confrontation would be catastrophic.
String of bombings
Wednesday's attack in Damascus was similar to one staged earlier this month in the same area that struck a building housing security staff for the army general headquarters, leaving two soldiers in critical condition.
Rebels have launched increasingly audacious attacks inside Assad's seat of power since expanding their presence in the city this summer.
In-depth coverage of escalating violence across Syria
An assassination bombing in central Damascus in July killed Assad's defence minister and brother-in-law.
Bombs planted by rebels exploded on Tuesday at a school building occupied by security forces and pro-government militias in Damascus.
The school's director told state television that seven people were wounded.
"At exactly 9:35am, seven improvised devices were set off in two explosions to target a school used for weekly planning meetings between shabbiha militia and security officers," Abu Moaz, a leader of rebel group Ansar al-Islam, said.
"There were several officers present, and we are hoping they will be part of a large number of killed in this operation."
While the 18-month conflict continued in Damascus, it also spilled over the border into Israeli-occupied territory for the first time.
Israel's military said Syrian forces fired mortar shells at villages suspected to be occupied by rebels but accidentally hit land in the disputed Golan Heights, causing no injuries or damage.
A spokesman said the Israeli military filed a complaint with UN forces responsible for monitoring the border area and that "fire from Syria leaking into Israel will not be accepted".