Former Syrian Vice-President Abdul Halim Khaddam says he wants to see President Bashar al-Assad ousted through a popular uprising.
Khaddam was at the heart of Syrian politics for over 20 years
Mr Khaddam told the BBC that Syrians were frustrated with the current regime and should be mobilised by the opposition groups in the country.
And he accused Mr Assad of being a traitor, denying he was one himself.
A UN inquiry implicated Syria in the murder of ex-Lebanese PM Rafik Hariri, but Damascus denies any involvement.
Speaking from Paris, where he has lived under protection since resigning his post in June 2005, Mr Khaddam said: "The Syrian people will take on themselves the responsibility for changing the government."
"Public opinion is very frustrated and the Syrian people are quite unhappy," he went on.
"There is an opposition in Syria which will find its way in leading the people to overthrow him."
'Don't care for power'
Mr Khaddam said he had not asked, or been asked by, other nations to help Syria's opposition.
"I have no relations whatsoever to do with any outside country, be they Arab or foreign. I work for the sake of Syria. I believe Syria will succeed in what it needs to do."
He told the BBC World Service that he expected democratic elections would be the "natural course" after any regime overthrow.
But he denied he would seek to be president himself. "I don't seek positions. I don't care for power."
Mr Khaddam confirmed he was interviewed by UN investigators earlier in the day.
"I told them what information I held about the assassination," he said, without clarifying whether that included his previous claim that President Assad had threatened Mr Hariri.
'Continue to kill'
He said that those in Syria who had described him as a traitor were doing so under pressure from Syrian intelligence.
"A traitor is he who causes harm to his country... The man who should be named as traitor is Bashar al-Assad himself," he said.
On Thursday, he told France 3 TV that the Syrian president should go to prison for his involvement in Mr Hariri's assassination in February.
President Assad has denied allegations linking him to the plot.
Mr Khaddam said he had not been surprised by the elimination of members of the Syrian opposition in Lebanon.
"Those who are behind the assassinations will continue to kill, because their goal is to cause chaos in Lebanon," he said.
"I am a target. My life is at risk, but I am not afraid."