The U.S.-backed alliance includes a Kurdish militia and Arab allies that joined it last year.
Russia's defense ministry also said in a statement that 69 rebels had handed themselves into the army.
President Bashar al-Assad, meanwhile, issued a decree offering an amnesty to rebels who surrender over the next three months
More than 280,000 have been killed and millions displaced in Syria's five-year conflict.
Nusra is listed as a terrorist organization by the United States and the United Nations.
Washingtons said it remains committed to the proposals reached by the United States and Russia to better enforce the cessation...
The Syrian army has dropped thousands of leaflets asking residents to cooperate with the military and calling on fighters to surrender...
The negotiations are based on "mutual interest to the extent and when and as we are able to identify that with the...
Tabqa would be a difficult military target because Islamic State has large stocks of weapons there.
The U.N. hopes to convene a new round of intra-Syrian peace talks in Geneva in August
Even he has refrained from voicing optimism, instead saying the effort was showing "a modicum of promise."