Updated

The Syrian regime seems on the verge of collapse. The killing of several key officials -- the defense minister and the president’s brother-in-law -- suggests that the regime that has already killed 17,000 could crumble far more quickly than most experts anticipated even a few weeks ago.

The next 36 hours are critical, Syria watchers say.

“Will the regime choose to massacre its way out of the crisis?” Andrew Tabler, an expert on Syria at the Washington Institute for Near East Policy and author of “In the Lion’s Den,” a book about life under Bashar Assad’s regime, said “And if it takes that path, will the army remain loyal and carry out its orders?”

Even Russian Foreign Minister Sergei Lavrov called today’s attack the beginning of a “decisive battle” between insurgents and the regime. But the carnage has not prompted Moscow to support a U.K- sponsored resolution that would set the stage for sanctions and even international military action against the minority Alawite regime if Assad fails to implement a six-point peace plan that he endorsed months ago, and has ignored ever since.

While the death of Syrian Defense Minister Daoud Rajiha, a Christian who had held his post for less than a year, got most of the initial headlines, the loss of Assef Shawkat, the president’s brother-in-law, is a far more debilitating blow to Damascus. Gen. Shawkat was not only the mastermind of the crackdown against the rebels, but the man who oversaw it.

A charter member of the regime’s inner circle, he was married to Assad's sister Bushra. He was among the more experienced members of President Assad’s team, having served as an adviser to Hafez al-Assad, President Assad’s father, who was known for his brutal suppression of a Sunni Muslim uprising in Hama in 1982. With the elimination of Shawkat and of other senior figures in the national security building when it was struck today, the regime’s security apparatus has been virtually decapitated.

Though reports of those killed and wounded were still being confirmed, Syrian sources and independent journalists reported that Hisham Ikhtiar, the director Syria’s national security chief, and Interior Minister Mohammad Ibrahim al-Shaar, were among those critically injured, and may have died in the attack.

The breach of security that allowed a rebel to take out so many key security officials as they met in a secure, three-story building in Rawda, near President Assad’s home, led U.S. Defense Secretary Leon Panetta to conclude that the situation in Syria is “rapidly spinning out of control.”

Appearing at a Pentagon news conference alongside U.K. Defense Minister Philip Hammond, Panetta said the bombings suggested that the regime was experiencing “fragmentation around the edges" in its 16-month struggle to retain power.

He said the bombings showed why the international community should bring "maximum pressure" on Assad to step down and permit a stable transfer of power.

Meanwhile, Special UN and Arab League envoy Kofi Anan struggled to offer the parties involved a diplomatic way out of the spiraling crisis by continuing to promote the peace plan that sent 300 international monitors to Syria 90 days ago. The monitors suspended their inspections weeks ago, saying that the violence made it impossible for them to operate.

But the unarmed monitors have still performed a variety of humanitarian functions and could now play an even more vital role if the regime collapses and Assad and his family decide to flee. The UN Security Council must vote by Friday on whether to extend the monitors’ mandate for another 90 days.

No one has seen Assad since the bombing and his current fate and state of mind are a source of intense speculation.

In Washington, attention has turned to the fate of Syria’s massive chemical stockpiles. Because Syria has not signed the Chemical Weapons Convention banning such weapons and its arsenals have never been inspected, intelligence analysts can only guess at their exact size and composition. But the Syrians are said to have produced and stored sarin and other lethal nerve agent, VX, mustard gas, and blister agents at at least three dozen sites throughout the country, as well as the missiles with which to deliver them. The Obama administration has long been concerned both about their possible use against Syrian citizens and the possibility that Hezbollah in Lebanon or other militant Islamists who have infiltrated the ranks of the rebels could seize them.

In recent days, some of these weapons have reportedly been moved, though Syria’s intentions in moving them are unclear. Nawaf Fares, Syria’s former ambassador to Iraq and the highest diplomat to defect to the rebels to date, said he feared that the regime might use these weapons against fellow Syrians if he were cornered. Israeli analysts, by contrast, say that the weapons have been moved to store them in more secure locations where rebel activity is less intense. Israel is even more concerned about what senior intelligence officials say is the infiltration of Syrian-controlled parts of the Golan Heights by Al Qaeda and other Islamist militants who have taken advantage of the security vacuum in Syria created by the regime’s relocation of armed forces in the Golan to areas where they are needed to fight the insurgency.

The Obama administration has warned Damascus that any use of chemical weapons would constitute a “red line,” though it is unclear what options are being considered if Assad crosses that line. The administration has been unwilling either to arm the rebels or contemplate military intervention in what the Red Cross pronounced a civil war last week, particularly not in an election year.

Syria watchers are also very concerned that a sudden collapse of the regime could trigger an escalation of sectarian slaughter in Syria, which is run by the minority Alawite sect. which is supported by many well armed minority groups that have traditionally sided with the regime – Christians, Druze, Kurds, to name but a few. But 70 percent of Syria's 26 million people are Sunni, and many fear sectarian slaughter if the Syrian state itself were to collapse.