The Syrian army is reported to have crossed into Raqqa Province after advancing in a major Russian-backed offensive against Islamic State (IS) militants.
The British-based Syrian Observatory for Human Rights says heavy Russian air strikes hit IS-held territory in eastern areas of Hama Province on June 3, allowing Syrian troops to reach the edge of Raqqa Province.
At least 26 militants and nine government troops and militia were killed in the army's advance, it said.
The city of Raqqa is further east and is the IS group's de facto capital in Syria.
Syrian army spokesmen were not immediately available for comment.
The IS group is also fighting Syrian troops, U.S.-backed fighters, and opposition militants in northern Syria and is facing an offensive by Iraqi government forces on their stronghold of Fallujah.