The Syrian army has advanced past the provincial borders of Raqqa which is the self-declared capital for Daesh caliphate, a London-based monitor says.
Troops on Saturday entered the Raqqa province for the first time since 2014, when Daesh unleashed its ferocious campaign of terror in the Arab country.
A potential recapture of Raqqa in Syria and Mosul in northern Iraq is seen as the ultimate blow to Daesh. In Iraq, armed fighters have edged as close as 30 kilometers (18 miles) of the capital of Nineveh province.
According to the so-called Syrian Observatory for Human Rights, government troops were advancing on the Tabqa dam on the Euphrates River, some 40 km (25 miles) from Raqqa, on Saturday.
"Regime troops backed by Russian airstrikes and Russian-trained militia entered Raqqa province on Saturday morning for the first time since August 2014," said the observatory's director Rami Abdel Rahman.
The advancements followed heavy aerial attacks carried out on Friday in the eastern areas of Hama province which borders Raqqa.
Tal Abyad was cleared of Daesh last year. The town served as a launchpad for Daesh attacks given its proximity to Raqqa.
Earlier in 2016, Syrian forces liberated the ancient city of Palmyra in the sprawling central Homs province.
Syria has been gripped by foreign-backed militancy it blames on some regional and western governments. According to a February report by the Syrian Center for Policy Research, the conflict in Syria has claimed the lives of over 470,000 people in total since March 2011.