[Updated at 11:25 a.m. ET] The U.S. government announced Wednesday a new round of sanctions against members of the Syrian government.

[Updated at 10:48 a.m. ET] Syrian Interior Minister Mohammad Ibrahim al-Shaar was also killed in today's explosion during a meeting of ministers and security officials in Damascus, according to Syrian-run media. That brings the death toll in the attack to four key members of President Bashar al-Assad's inner circle.

[Updated at 10:01 a.m. ET] The Free Syrian Army says today's deadly blast targeting a meeting of ministers and security officials was a planted bomb and not a suicide attack as previously reported on Syrian-run media.

"It was an explosive device planted inside the meeting room and triggered with a remote control," the deputy head of the opposition Free Syrian Army, Col. Malek al-Kurdi, told CNN.

[Updated at 9:39 a.m. ET] Hasan Turkmani, Syrian president Bashar al-Assad's security advisor, was among those killed in the Damascus blast Wednesday, according to state television. Turkmani was Syria's former defense minister.

[Updated at 9:25 a.m. ET] The attack, during a meeting of ministers and security officials, was coordinated by several rebel brigades in Damascus, the deputy head of the opposition Free Syrian Army, Col. Malek al-Kurdi, told CNN.

The colonel told CNN that there is an "extensive" gun battle going on between defected officers, with the help of the Free Syrian Army against Assad's Republican guard and elite forces.

"We may see a breakthrough sooner than we expected," he said.

The most senior Syrian diplomatic defector Nawaf Al Fares, who was recently Syria's Ambassador to Iraq, told CNN he believed the attack was extremely significant.

"I think what happened today is a big and important operation that hit the heart of the regime. I believe the regime will escalate against the Syrian people, but at the same time it started getting weaker and weaker," he said. "The ability of the rebels to reach to this place in this way is a great achievement."

The attack represents "a massive psychological blow to the regime" and will accelerate al-Assad's "demise," said Anthony Skinner, an analyst with the think tank Maplecroft.

It could suggest that, after a 16-month relentless uprising, "the regime itself is crumbling," said Rime Allaf, an analyst with Chatham House.

Events on the ground in Syria show "a real escalation in fighting," said U.S. Defense Secretary Leon Panetta.

It "tells us that this is a situation that is rapidly spinning out of control, and for that reason it's extremely important that the international community, working with other countries that have concerns in that area, have to bring maximum pressure on Assad to do what's right, and to step down and to allow for that peaceful transition. "

[Posted at 8:43 a.m. ET] Syria's defense minister and deputy defense minister were killed Wednesday in a blast at a national security building in Damascus, state media reported.

The attack brings the bloodshed in Syria well into President Bashar al-Assad's inner circle and could mark a pivotal point in the 16-month uprising.

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Defense Minister Dawood Rajiha and Deputy Minister Assef Shawkat - who is al-Assad's brother-in-law - were killed in the explosion during a meeting of ministers and security officials, state TV reported.

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They are the highest-ranking Syrian officials killed in the uprising.