Syrian authorities have arrested four lawyers who supported unprecedented protests demanding political freedoms and an end to corruption, rights defenders said on Tuesday.

Their arrest came as President Bashar al-Assad, facing the biggest challenge to his rule from protests that spread from the southern city of Deraa, promised to study granting more freedom to Syrians, who have been ruled by the Baath Party since it took power in a 1963 coup and imposed emergency law.

One of the lawyers, Hussein Issa, was arrested on Sunday outside the Palace of Justice in the Syrian capital, the activists said.

Issa was leaving the compound after submitting papers in defence of protesters who staged a silent demonstration for the release of political prisoners and of 15 children arrested in Deraa for writing freedom slogans on school walls, they said.

The silent protest in Marjeh Square in Damascus took place two days before the demonstrations erupted in Deraa on March 18.

A lawyer from Deraa, Thamer al-Jahmani, was also arrested on Sunday after he made statements to the press in support of his home city. Two lawyers, Suleiman al-Nahili and Nidal al-Sheikh Hamoud were arrested as they marched on Friday in a demonstration in the city of Homs in support of Deraa.

Syria's ruling hierarchy has a history of imprisoning lawyers, despite condemnation of the practice by the International Lawyers Union and international rights group.

Leading lawyers Anwar al-Bunni and Mohannad al-Hussani, who have spent their life defending political prisoners, are serving five and three-year sentences respectively for "weakening national morale".

The two are winners of prestigious rights awards, together with 80-year-old lawyer and former judge Haitham al-Maleh, who spent nearly a year in jail before he was released under an amnesty marking the anniversary of the coup which brought the Baath Party to power.