A gathering of a dozen liberal, pan-Arab nationalist, and left-wing political parties on Sunday, said they signed a petition named the Damascus Declaration to promote greater freedoms and demand a new constitution to usher in political pluralism.
"We are calling for ending of all forms of political repression and opening a new chapter in the history of the country," Akram al-Buni, an activist among the signatories said.
The alliance, which also includes both Arab and Kurdish leftist activists, urged the government to lift the emergency law, in place since the ruling Baath party assumed power in 1963.
"We demand the abrogation of all forms of exceptions in public life and the end of emergency laws and extra-ordinary judicial courts and the release of all political prisoners," said the statement.
Syria, whose Baath party agreed in June to loosen the emergency law, is under mounting US-led pressure to reform.
But the authorities in the tightly controlled country say they cannot tolerate foreign inspired activism that seeks to reap political gains from mounting US and Western pressure to isolate the country.
Bashar al-Assad's government
faces US-led pressure to reform
Activists said police disrupted a meeting on Sunday to launch the alliance in the office of 72-year-old lawyer Hasan Abd al-Azim, who also heads a pan-Arab nationalist party.
Abd al-Azim said the grouping was the secular opposition's first serious attempt to put forward unified demands for reforms since President Bashar al-Assad introduced a measure of political freedom when he assumed power in 2000.
The normally squabbling groups also seek to include Syrian dissidents abroad who seek reforms through peaceful means, Abd al-Azim added.
Previous attempts to bring together the secular and leftist groups had failed over a host of ideological and organisational differences.
The alliance does not include the banned Muslim Brotherhood whose membership was made a capital offence in 1980 after crushing a revolt by Islamists against the secular Baath party.
"We are calling for ending of all forms of political repression and opening a new chapter in the history of the country"
Aljazeera's correspondent in Syria reports that the alliance includes Kurdish parties, al-Mustaqbal (Future) party and civil society committees.
The authorities have said they plan to allow the creation of opposition political parties, as long as they are not religiously or ethnically based. The Baath party, however, is expected to retain its political dominance.
The liberal opposition say continued arrests of its members in the past few months were aimed at sending a message to Syrian activists that they were not ready to tolerate any attempt to exploit the foreign pressure to undermine the Baath party.
"It is a message to the opposition that the state is still strong and would only permit what it wants and would continue arrests and bar public meetings," said al-Buni.
The authorities have in recent weeks barred several public meetings by the secular liberal opposition organised to discuss greater democratisation on the pretext they did not have legal permission.