A key activist in Syria's "tolerated" opposition said Saturday he cannot attend peace talks in Moscow next week because Damascus refuses to lift his travel ban.

"Neither I nor my movement will take part in the meeting in Moscow because the regime refuses to lift my travel ban," Louay Hussein told AFP.

Hussein, who heads the Building the Syrian State party, said last week that he hoped to attend the talks being hosted by Moscow Monday through Thursday.

He said Russia, a key ally of President Bashar al-Assad, had invited him to the discussions and that he had planned to attend with party representatives Mona Ghanem and Anas Judeh.

But Hussein, who was released in February from three months in jail, remains under a travel ban pending a verdict in a case in which he is accused of having "weakened national sentiment".

The verdict is expected on April 29.

Another key domestic opposition group, the National Coordination Committee for Democratic Change, will be attending the Moscow talks.

Its chief, Hassan Abdel Azim, will participate with four other members of the organisation, according to executive committee member Yehya Aziz.

The Syrian government is expected to be represented by its UN envoy, Ibrahim Jaafari.

The meetings are expected to cover the humanitarian situation in the country, as well the possibility of restarting talks within the framework of an agreement reached during negotiations in Switzerland.

But the key exiled opposition body, the National Coalition, has said it will not attend, accusing Russia of merely seeking to bolster the regime.

More than 215,000 people have been killed in Syria since the conflict began with peaceful anti-government protests in March 2011, before spiralling into a war after a regime crackdown.