BEIRUT — An audacious bombing aimed at the heart of Syria's feared security services killed three high-ranking officials in Damascus and left President Bashar Assad's grip on power appearing more tenuous than at any time during the 16-month uprising against his family dynasty.
Government reinforcements were reported to have been deployed in the streets of Damascus on Wednesday, a fourth day of fighting in the capital, which had largely been spared the violence racking much of the country.
The attack on national security headquarters was a graphic illustration of the shifting momentum in the conflict. It demonstrated that the decentralized and often ragtag rebel force, which has been battling security forces in the provinces for months, had succeeded in taking the fight to Assad's doorstep, as it had long vowed to do.
And it exposed the inability of the Syrian security apparatus, long regarded as among the most effective and feared in the Middle East, to protect its own key leaders, much less put down a popular uprising.
But few were predicting that Assad's regime would fall quickly or easily.
The bombing killed Syria's defense minister, Daoud Rajha, and his deputy, Gen. Asef Shawkat, who reportedly was married to Assad's older sister and was a member of the president's inner circle. It also killed Gen. Hassan Turkmani, a former defense minister who served as an assistant vice president. Interior Minister Maj. Gen. Mohammad Ibrahim Shaar was injured.
Rumors swirled that Assad had left the capital or was preparing to declare a national state of emergency. The president did not appear on state television, fueling the rumor mill. Another rumor had his wife, Asma, leaving for Moscow. There was no confirmation of any of the reports.
State media reported that Assad had issued two decrees after Wednesday's attack. He appointed Gen. Fahd Jassem Freij as the new defense minister.
The Free Syrian Army, the main umbrella rebel group, took responsibility for the strike and warned that more bombings were planned. It did not say how it managed to infiltrate the security establishment and plant the bomb. Official Syrian media initially said a suicide bomber was responsible, but later described the attack only as a bombing.
One of the rebel group's strategists confidently told Egyptian television that Assad's government was on course to collapse "within two months." Also claiming credit for the blast was an Islamist group, Liwa al-Islam, or Brigade of Islam.
The confluence of heavy fighting in the capital and the bombing suggested for the first time in the conflict that Assad may be losing control and that the repressive infrastructure central to maintaining more than 40 years of family rule could be coming apart.
U.S. Defense SecretaryLeon E. Panettasaid in Washington that the bombing marked "a real escalation in the fighting" and that the situation in Syria was "rapidly spinning out of control."
"Assad's brother-in-law was one of the most powerful hard-line officials in the country. If the Free Syrian Army can get to him in Damascus, that is extraordinary," said a senior Obama administration official, who spoke on condition of anonymity. "If I'm some senior regime official and I'm thinking about my future, this would weigh heavily on me."
However, even many opposition activists said they expected a hard fight ahead.
"I think we are coming near the end," Yassin Haj Saleh, an opposition author and columnist, said in an email from Damascus. "But there are still more pains in the coming days and weeks."
Despite Wednesday's losses, most of Assad's inner core of hard-line supporters remains in place. Chief among them is his brother, Maher, who commands an important brigade.
Many of the highest-ranking officers are members of Assad's minority Alawite sect, an offshoot of Shiite Islam. Many Alawites are fiercely loyal to Assad and have come to view the conflict as a fight for survival — as do many Christians, who fear that Assad's downfall could bring in an Islamist government intolerant of minorities. Rajha, the defense minister who died, was the highest-ranking Christian in the government.
The insurgency is dominated by members of Syria's Sunni Muslim majority.
In the field, regular forces maintain a substantial edge in firepower over the insurgents, who are mostly armed with rifles. The reported use of helicopter gunships and armored vehicles in the capital this week underscores the disparity in strength. Rebel groups have complained bitterly about not having the arms to take on helicopters and tanks.
But a steady stream of defections has weakened the Syrian military. Each day brings new reports of desertions, often from the ranks of Sunni Muslim conscripts and officers. Defectors report that morale is low and the quality of equipment is eroding as the military grapples with a rebellion that has practically spread to the four corners of the country.
It was not clear whether the bombing was part of the broader rebel offensive in Damascus or whether it was planned and launched separately.
Opposition activists and the government were reporting intense clashes on the ground in Damascus, where the government was said to be using artillery and helicopter gunships to put down uprisings in a growing number of neighborhoods. The reports could not be independently confirmed.
The state news service reported that the military "chased down terrorists" in the Midan neighborhood, an opposition hot spot near the Old City walls, "and killed and arrested a large number of them."
At least one rebel leader has declared that the "liberation" of Damascus was in progress. But the scattered fighting did not necessarily suggest a coordinated series of attacks.
For months, insurgents have been assassinating security officers viewed as "collaborators" with the Assad government. The president calls the guerrillas "terrorists" and has vowed to defeat them.
The bombing occurred as the issue of Syria was again coming before the United Nations. Even though they have long discouraged talk of military intervention, the United States and its allies seeking Assad's ouster are calling for economic sanctions against Syria tied to a chapter of the U.N. charter that allows for the use of force.
But Russia, which holds a veto on the U.N. Security Council, has objected to sanctions. The U.N. agreed to put off discussion of the matter until Thursday.
President Obama and Russian President Vladimir Putin spoke Wednesday by phone about Syria at Obama's initiative. No details were provided. Publicly, Russia condemned the bombing and accused Western powers of inciting the uprising against Assad.
Sandels is a special correspondent. Times staff writers Ken Dilanian in Washington and Sergei L. Loiko in Moscow contributed to this report.