A key member of Syrian President Bashar al-Assad’s regime has defected, a Western diplomat said Friday, a stunning blow to the embattled government.

He is Brig. Gen. Manaf Tlas, a Republican Guard military commander, the son of a former defense minister and possibly the most senior Sunni in a power structure dominated by the Alawite minority.

“He’s an inside confidant of Assad. So it counts that even an insider thinks it’s time to go,” said the official, who spoke on condition of anonymity. The official was not authorized to speak to the media.

Syria has been engulfed in nearly 16 months of unrest resulting in thousands of deaths. The defection comes as government assaults against protesters led to a nationwide uprising.

Tlas has been estranged from the regime over the killing of Sunnis, the official said. His father, former Defense Minister Mustafa Tlas, and the rest of his family are in Paris, the official said.

Reports of Tlas’ defection first surfaced Thursday. Western officials are saying he is on his way to Paris. It is not known whether he has joined the opposition.

Rafif Jouejati, spokeswoman for the opposition Local Coordination Committees of Syria, called the development “quite significant.”

“It signals that the domino effect of defections is speeding up as longtime regime supporters and collaborators realize that Assad’s ship is sinking fast. Expect more defections in the coming days as the regime accelerates its scorched-earth policy in a desperate attempt to destroy as much as possible before falling apart,” she told CNN.

Jeffrey White, a defense fellow at the Washington Institute for Near East Policy, called the development “an important event.”

READ MORE: CNN