This is the most significant act of Syria's Revolution so far

There's no question.

This is the most significant act of Syria's Revolution so far.

There have been greater explosions this year, killing more people, even in the heart of Damascus.

But never before have Syria's rebels penetrated the very heart of President Assad's inner circle.

It is the location and the seniority of the dead that make this the biggest blow Assad has yet suffered.

President Assad with senior military officials including General Rajiha Credit: Reuters

He has lost his brother in law.

General Assef Shawkat was a big dog in Damascus; married to Bushra, Bashir's sister; a former Head of Military Intelligence and the current Deputy Chief of Staff of the Army.

President Assad's brother-in-law Assef Shawkat was killed in the attack Credit: Reuters

Dead alongside him was Daoud Rajiha the Defence Minister and the most senior Christian in the Government; a man whose very presence allowed the Alawite regime to claim all Syrians were represented in the government.

Syria's Defence Minister Daoud Rajha has been killed in an explosion in Damascus Credit: Reuters

Also killed, a senior General who was a close aide to Assad.

They were killed, according to the group that is claiming this attack, not by a suicide bomber, but by a bodyguard in Assad's inner circle, one of a group of rebels who had been planning this attack for a month.

The Generals and Intelligence chiefs would surely have been discussing the fighting raging just a couple of miles from where they were meeting, inside the capital.

Earlier, they would have ordered the tanks onto the streets of Damascus to fire at rebels.

They would have known this was becoming a fight for their own survival.

The blow to Assad and his inner circle cannot be underestimated.

They have been shaken, quite literally, by this.

US Defence Secretary Leon Panetta says the situation in Syria is now spinning out of control.

Finally, with this attack, that must have dawned on the President in his palace.