Syrian opposition figures on Wednesday urged embattled President Bashar Al-Assad to ensure a transition to democracy as demanded by protesters or face the collapse of his 11-year regime.

As a military assault on the restive town of Daraa entered a third day, the National Initiative for Change said a democracy would "safeguard the nation from falling into a period of violence, chaos and civil war."

"Either the ruling regime leads itself in a peaceful transition towards democracy... or it will go through a process of popular protests that will evolve into a massive and grassroots revolution that will breakdown the regime and carry Syria through a period of transition after a wave of violence and instability," the statement said.

"If the Syrian president does not wish to be recorded in history as a leader of this transition period, there is no alternative left for Syrians except to move forward along the same path as did the Tunisians, Egyptians and Libyans before them," it added.

Syria has been rocked by massive pro-democracy protests since mid-March in which at least 400 people have been killed, according to human rights activists.

Protesters have taken to streets even after Assad scrapped nearly five decades of draconian emergency rule and abolished the repressive state security court on Thursday last week.

Syrian forces launched a bloody assault on the protest hub of Daraa, south of Damascus, leaving more than 30 people dead.

Western nations, human rights group and the United Nations have expressed alarm over the Syrian crackdown.

On Tuesday, UN Secretary General Ban Ki-moon said he was watching events in Syria "with increasingly grave concern," after briefing the 15-nation Security Council about the crisis in the Arab world.

"I condemn, utterly, the continuing violence against peaceful demonstrators, most particularly the use of tanks and live fire that have killed and injured hundreds of people," he added.