Government forces struck back against rebels with attack helicopters and shelling in a fifth straight day of clashes in Damascus. The inability of the military to control the clashes in the capital against lightly armed rebel forces and the deadly bombing of a high-level security meeting a day earlier made Assad's hold on power look increasingly tenuous.
The whereabouts of Assad, his wife and their three young children have been a mystery since the attack that killed his brother-in-law and his defense minister. Assad does not appear in public frequently, and his absence was notable following such a serious blow his inner circle.
The state TV announcement appeared aimed at sending the message that Assad is alive, well and still firmly in charge. It said Assad wished the new defense minister good luck but it did not say where the swearing-in took place. Nor did it show any photos or video of the ceremony, as it usually would.
Thousands of Syrians streamed across the Syrian border into Lebanon, fleeing as fighting in the capital entered its fifth straight day, witnesses said. Residents near the Masnaa crossing point - about 25 miles (40 kilometers) from Damascus - said hundreds of private cars as well as taxis and buses were ferrying people across.
Wednesday's rebel bomb attack struck the harshest blow yet to Assad's regime. The White House said it showed Assad was "losing control" of Syria.
Syrian TV confirmed the deaths of Defense Minister Dawoud Rajha, 65, a former army general and the most senior government official to be killed in the rebels' battle to oust Assad; Gen. Assef Shawkat, 62, the deputy defense minister who is married to Assad's elder sister, Bushra, and is one of the most feared figures in the inner circle; and Hassan Turkmani, 77, a former defense minister who died of his wounds in the hospital.
Also wounded were Interior Minister Mohammed Shaar and Maj. Gen. Hisham Ikhtiar, who heads the National Security Department. State TV said both were in stable condition.
Rebels claimed responsibility, saying they targeted the room where the top government security officials in charge of crushing the revolt were meeting.
Maj. Gen. Robert Mood, the Norwegian head of nearly 300 unarmed U.N. observers in Syria, condemned the violence and encouraged a diplomatic solution, which appears increasingly out of reach. He spoke just hours before a planned U.N. Security council vote on whether to renew the mission's mandate, which expires Friday, and impose new sanctions on the Damascus regime.
"It pains me to say, but we are not on the track for peace in Syria," Mood said in Damascus.
The UN vote had been scheduled for Wednesday, but was postponed after key Western nations and Russia failed to agree the text of a resolution aimed ending the escalating violence. Russia, a longtime ally of Syria, has stood by the Syrian regime and vowed to veto any measures that could lead to international military intervention.
In Thursday's fighting in Damascus, government forces fired heavy machine guns and mortars in battles with rebels in a number of neighborhoods in the capital, the Britain-based activist group Syrian Observatory for Human Rights said.
Adding to the confusion, Syria's state-run TV warned citizens that gunmen were disguising themselves in military uniforms to carry out attacks.
"Gunmen are wearing Republican Guard uniforms in the neighborhoods of Tadamon, Midan, Qaa and Nahr Aisha, proving that they are planning attacks and crimes," SANA said.
Many residents were fleeing Damascus' Mezzeh neighborhood after troops surrounded it and posted snipers on rooftops while exchanging gunfire with opposition forces.
The Observatory, which relies on a network of activists inside Syria, said rebels damaged one helicopter and disabled three military vehicles.
Rebels fired rocket-propelled grenades at a police station in the Jdeidet Artouz area, killing at least five officers, the group said.
Activist claims could not be independently verified. The Syrian government bars most media from working independently in the country.
The unarmed observers were authorized for 90 days to monitor a cease-fire and implementation of Kofi Annan's six-point peace plan, but the truce never took hold and the monitors have found themselves largely locked down because of the persistent violence.
Mood said the observers "will become relevant when the political process takes off."
Syria's 16-month crisis began with protests inspired by the Arab Spring wave of revolutions, but it has evolved into a civil war, with rebels fighting to topple Assad.