The Syrian Observatory for Human Rights reported "fierce clashes" as it said regime ground troops penetrated Khan Sheikhun in Idlib province for the first time since they lost control of it in 2014
Syrian regime forces entered a key north-western town on Sunday amid intense fighting with jihadists and their rebel allies which has left dozens of combatants dead, a war monitor said.
The Syrian Observatory for Human Rights reported "fierce clashes" as it said regime ground troops penetrated Khan Sheikhun in Idlib province for the first time since they lost control of it in 2014.
The latest fighting, which broke out overnight Saturday to Sunday, has already killed at least 59 jihadists and allied rebels as well as 28 members of pro-regime forces, the Britain-based monitor said.
Pro-regime forces have been advancing over the past few days in a bid to encircle Khan Sheikhun from the north and west and to seize a key highway.
The road runs through Idlib, connecting government-held Damascus with the northern city of Aleppo, which the regime retook from rebels in December 2016 after a pulverising Russian-backed offensive.
On Sunday they retook the village of Tel al-Nar and nearby farmland northwest of Khan Sheikhun before closing in on the town, Observatory head Rami Abdel Rahman said.
They then advanced into the north-western districts of the town amid "ferocious resistance" from jihadists and allied rebels, he said.
Jihadist group Hayat Tahrir al-Sham, led by Syria's former Al-Qaeda affiliate, carried out several suicide bombings to slow the advance of regime troops, Abdel Rahman added.
HTS controls most of Idlib province as well as parts of the neighbouring provinces of Hama, Aleppo and Latakia.
A buffer zone deal brokered by Russia and Turkey last year was supposed to protect the Idlib region's three million inhabitants from an all-out regime offensive, but it was never fully implemented.
Regime and Russian air strikes and shelling since late April have killed more than 860 civilians, according to the Observatory, which relies on sources inside Syria for its information.
On Sunday air strikes by the Syrian regime and its ally Russia killed two people, including a child, in the south of Idlib, the Observatory said.
More than 1,400 insurgents and over 1,200 pro-regime forces have been killed since April, according to the monitor.
The violence has displaced more than 400,000 people, the United Nations says.
Khan Sheikhun was hit by a chemical attack that killed more than 80 people in April 2017, attributed to the Syrian regime by the UN and international experts.
In response, US President Donald Trump ordered strikes on the regime's key Shayrat airbase.
Now almost emptied of inhabitants, Khan Sheikhun sheltered almost 100,000 people before the start of the current military escalation, the majority displaced from Hama province.
"Many of these people have been displaced up to five times," the UN's regional spokesman for the Syria crisis, David Swanson, told AFP on Saturday.
"Ongoing clashes, shelling and air strikes, including the use of barrel bombs, continue unabated" and have damaged schools and hospitals, he added.
Syria's conflict has killed more than 370,000 people and displaced millions at home and abroad since starting with the brutal repression of anti-regime protests in 2011.