The head of the Syrian regime's crisis cell, General Hassan Turkmani, was killed in a Damascus attack on the National Security headquarters on Wednesday, the Syrian Observatory for Human Rights said.
Lebanon's Hezbollah-owned television station Al-Manar also reported the death of Turkmani, a former defence minister, hours after the current defence minister and President Bashar al-Assad's brother-in-law were confirmed dead in the same attack.
The Syrian authorities have not confirmed Turkmani's death, though they did state earlier that several officials were badly wounded in the attack.
"General Hassan Turkmani, currently assistant to the Syrian vice president, has died from wounds he sustained as a result of the blast," the Observatory said, citing sources in Damascus.
He was the third official to be killed on Wednesday, in an operation claimed by the rebel Free Syrian Army.
The FSA command announced "the good news of the outstanding operation this morning that targeted the National Security headquarters and the killing" of the officials "responsible for barbaric massacres."
Officials said a suicide bomber struck as ministers and security officials were meeting at the heavily guarded site, but the FSA did not say how the officials were killed.
Defence minister General Daoud Rajha and Assad's brother-in-law Assef Shawkat were killed and interior minister Mohammed al-Shaar and General Hisham Ikhtiyar, head of National Security, were wounded, state television and security officials said.