Hayat Tahrir al-Sham (HTS), a jihadist group led by Syria’s former Al-Qaeda affiliate, has since January controlled most of Idlib province as well as parts of neighbouring Hama, Aleppo and Latakia provinces.
Several other armed rebel groups also operate in the area.
Fighting in various parts of the region on Saturday claimed the lives of 23 pro-government forces as well as 32 jihadists and allied rebels, the Syrian Observatory for Human Rights said.
The regime also launched dozens of air strikes against northern Hama and southern Idlib, the Britain-based monitor added.
The latest violence came as forces loyal to Damascus pushed a days-long advance towards a strip straddling the provinces of Hama and Idlib, it said.
They aim to capture Kafr Zita — one of the largest towns in northern Hama — and the nearby village of Al-Latamneh from jihadists and rebels, said Observatory head Rami Abdel Rahman.
Both lie on the southern edge of the jihadist-run bastion of Idlib, one of the last centres of opposition to President Bashar al-Assad after eight years of civil war.
Regime forces have closed in Kfar Zeita and Latamneh over the past week, after capturing a string of nearby towns and villages, the Observatory said.
They are also trying to surround the nearby town of Khan Sheikoun in order to wrest it from the jihadists, Abdel Rahman said.
The latest advances come after the Syrian government on Monday scrapped a brief three-day ceasefire for the Idlib region, accusing its opponents of refusing to abide by the truce.
The region was supposed to be protected from a massive government offensive by a Turkish-Russian buffer-zone deal that was reached in September last year.
But it has come under increasing bombardment by Damascus and its backer Moscow since the end of April that has killed, according to the Observatory, more than 800 civilians.
Nearly 80 people have lost their lives in retaliatory fire on regime-held territory in that same period, it said.
The violence has also pushed 400,000 people from their homes, according to the United Nations.
Syria’s conflict has killed a total of more than 370,000 people and displaced millions since it started with the brutal repression of anti-government protests in 2011.