The party leadership on Sunday said in a statement carried by the official SANA news agency: "The national leadership has decided to throw Khaddam out of the party. It considers him a traitor. Khaddam has betrayed the party, the homeland and the (Arab) nation."
The party, which has ruled Syria with an iron grip since 1963, described Khaddam's comments to Al-Arabia, the Dubai-based satellite channel, from his base in exile in Paris as a "slander which violates the principles of the nation".
Khaddam, in the interview, accused Bashar al-Assad, the Syrian president, of threatening al-Hariri just months before his murder, dealing a fresh blow to the increasingly pressurised Syrian government.
Members of Syria's loyalist parliament had earlier called for Khaddam to be tried for treason for his bomb shell, the first time in the government's history such a high-ranking official turned whistleblower.
MPs unanimously passed a motion calling for a trial during a regular session in which several MPs accused Khaddam of "treason" and "corruption" for his remarks.
Khaddam, long the architect of Syria's military and political domination of neighbouring Lebanon, made his explosive accusations in an interview broadcast by Al-Arabiya on Friday.
Khaddam, 73, announced his shock resignation as vice-president at a Baath party congress in June.
Emile Lahoud (R) was accused of
turning al-Assad against al-Hariri
"I will destroy anyone who tries to hinder our decisions," Khaddam quoted al-Assad as telling al-Hariri during a meeting in Damascus.
Khaddam, speaking from Paris where he and his family now live, said the meeting took place a few months before the 14 February assassination of al-Hariri in a Beirut bomb blast for which a UN inquiry has implicated Syrian intelligence.
"We must await the results of the investigation, but no Syrian security service could take such a decision unilaterally," Khaddam said.
In the same interview, he also accused Emile Lahoud, Lebanon's pro-Damascus president, of turning al-Assad against al-Hariri with a calculated series of attacks on his conduct as prime minister, a charge that Lahoud's office vigorously denied on Sunday.