Syrian opposition groups meeting in Turkey have insisted on regime change.
This demand comes a day after President Bashar al-Assad decreed an amnesty for political prisoners following two months of bloodshed.
The three-day gathering, 'Conference for Change in Syria', opened with the Syrian national anthem and a minute of silence for 'the martyrs' killed in bloody crackdowns on street protests simmering in Syria since March.
Speakers at the conference condemned 'massacres' of civilians and urged Assad's departure.
Syrian state television meanwhile said an investigation had been launched into the death of a 13-year-old boy who was allegedly tortured and killed by security forces in Daraa, south of Damascus.
State television said the interior ministry had appointed a commission to investigate the death of Hamza al-Khatib, 13, after pro-democracy activists set up a Facebook page and called for fresh protests in his memory.
Yesterday, Syrian President Bashar al-Assad had issued a general amnesty after weeks of protests against his rule and a violent military crackdown.
The amnesty covers 'all members of political movements, including the Muslim Brotherhood', state television reported.
Membership of the brotherhood, which led an armed uprising against Mr Assad's father in 1982, is punishable by death in Syria.
Mr Assad's move was the latest in a series of reforms - including lifting a 48-year state of emergency and granting citizenship to stateless Kurds in eastern Syria - aimed at addressing the grievances of protestors.
But those steps have been accompanied by a ruthless military crackdown in which rights campaigners say 1,000 civilians have been killed and more than 10,000 people arrested.
Meanwhile, Britain believes that Syria should be reported to the UN Security Council over its alleged illicit nuclear activity.
In a restricted report circulated to member states last week, the UN watchdog said it was 'very likely' that a remote desert site in Syria bombed by Israeli planes in 2007 was indeed a covert nuclear reactor, as alleged by the US.