Syrian defense minister and Assad relative killed in suicide blast SANA via Reuters, file Syrian Defence Minister Dawoud Rajha attends a dinner in honour of army officers in Damascus on the anniversary of the 65th Army Foundation in this August 1, 2010 file photo. By NBC News' Ayman Mohyeldin and wire services Updated at 9:15 a.m. ET: Syria's defense minister and President Bashar Assad's brother-in-law were killed in a Damascus suicide bomb attack carried out by a bodyguard on Wednesday, state television reported, the most serious blow to Assad's high command in the country's 16-month-old rebellion. The bomber -- said by a Reuters security source to be a bodyguard assigned to Assad's inner circle -- struck during a meeting attended by ministers and senior security officials in the Syrian capital as battles raged within sight of the presidential palace. Assad appointed him to the post last year. Within hours, Syrian State TV announced that Brig. Gen. Fahed Jassim el Friej would replace Rajha. Assad's brother-in-law Assef Shawkat -- widely seen as a member of the president's inner circle -- was also reportedly killed in the attack. After years as deputy head and then chief of military intelligence, he was appointed deputy defense minister, a position that allowed him to wield power out of the limelight. U.S. diplomatic cables published by Wikileaks described Shawkat as a clever, well-read officer who was part of Syria's "killing problem." A senior officer with the Free Syrian Army claimed responsibility for the high-level assassinations, a decisive moment in the conflict. AFP - Getty Images, file A file picture taken on June 13, 2000 shows General Assef Shawkat, the brother-in-law of Syrian President Bashar al-Assad, who was killed Wednesday. The death of two of the regime's most senior operational commanders could seriously dent the effectiveness of Assad's army, as it fights battles across the capital. Blast kills Assad brother-in-law, Syria's shadowy enforcer Later Wednesday, there were reports of explosions at the headquarters of the army's fourth division in Damascus, which is led by Assad's younger brother Maher, considered the second most powerful man in Syria. It was not clear whether those forces were being targeted. Syria's information minister denied on state television that any explosion had occurred at the base. The capital has seen days of clashes pitting government troops against rebels. Activists in Damascus said by telephone that Republican Guards sealed off the Shami hospital in the capital after ambulances had brought casualties from the site of the explosion. In addition to weakening the army command, Wednesday's killings are bound to heighten a sense of paranoia and mistrust among Assad's top ministers and officials. The attack is unlikely to have been planned by just one person. Assad's next moves will be crucial. Failure to appear in public, or at the funerals of the two men, could be seen as a sign of a weakening regime. The revolt came within sight of Assad's presidential palace Wednesday as fighting erupted in major Damascus neighborhoods for a fourth day. Photoblog: Who are the Syrian rebels? An army barracks near the "palace of the people," a huge Soviet-style complex overlooking the city from the western district of Dummar, came under rebel fire around 7:30 a.m. "I could hear the sound of small-arms fire and explosions are getting louder and louder from the direction of the barracks," Yasmine, who works as an architect, said by phone from Dummar. Video footage broadcast by activists purportedly showed a fire in the barracks overnight as a result of an attack by mortar rounds, but residents who saw the fire said they had not heard explosions to indicate it was a result of an attack. Fighting in Sunni areas Fighting also erupted overnight in the southern neighborhoods of Asali and Qadam, and Hajar al-Aswad and Tadamun -- mainly Sunni Muslim districts housing Damascenes and Palestinian refugees. PhotoBlog: Behind Syrian rebel lines Government troops used heavy machine guns and anti-aircraft guns against rebels moving deep in residential neighborhoods, armed mostly with small arms and rocket-propelled grenades. Syrian TV via AFP - Getty Images An image taken from Syrian TV shows security forces during armed clashes with gunmen the TV called "terrorists" (unseen) in the Al-Midan district of Damascus on Wednesday. Army tanks and anti-aircraft guns, used as an infantry weapon, took positions in the northern neighborhood of Barzeh, where hundreds of families from the neighboring district of Qaboun are seeking shelter.