Ahrar al-Sham and the Jaish al-Islam, two terrorist groups fighting to overthrow Assad, agreed to take part in UN-sponsored peace talks in Geneva.
But the Syrian government and its close ally Russia view both as terrorist groups that should be excluded from the process, along with the Daesh (ISIL) group and al-Qaeda's local affiliate.
Information Minister Omar al-Zoubi's comments to Syrian TV Sunday came as the main opposition delegation arrived in Geneva, the Associated Press reported.
The delegation has named Jaish al-Islam official Mohammed Alloush as its chief negotiator.
Most parties agree that Daesh and the al-Qaeda-affiliated Nusra Front should be excluded.