"There are 28 opposition figures who have received an invitation to the planned Moscow meeting," the source said, speaking on condition of anonymity.
They include the head of the key Syrian National Coalition opposition grouping, Hadi al-Bahra, as well as two former Coalition chiefs, Moaz al-Khatib and Abdel Basset Sida.
The list also includes members of the tolerated domestic opposition, including Hassan Abdel Aazim, Aref Dailia and Fateh Jamous.
Qadri Jamil, a former deputy prime minister who was sacked in 2013 and has good ties with Russia, was also invited.
It was not immediately clear whether any of the invitations had been accepted.
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The Coalition's general assembly is due to meet in Turkey for three days beginning Friday and is expected to discuss the invitations.
Russia, a key backer of Syrian President Bashar al-Assad, has been trying to relaunch peace talks that would include meetings between delegates of the regime and the fractured opposition.
In December, the foreign ministry said Moscow planned to host opposition delegations in late January, possibly followed by a visit by regime representatives that could bring the two sides together for talks.
Several opposition groups are also expected to meet in Cairo in coming weeks to form a unified front, according to opposition sources, though a timetable and list of participants has not been made public.
More than 200,000 people have been killed in Syria since the beginning of the conflict in March 2011.
Two successive rounds of UN-brokered talks between the regime and opposition failed to achieve agreement.