Syrian troops and allied fighters advanced Saturday to capture most of Albu Kamal, a monitor said, in a tug-of-war over the Islamic State group's last urban stronghold in the country.
The town in Syria's oil-rich Deir Ezzor province has changed hands several times, with government troops announcing its capture but losing it to a blistering IS counter-attack a week ago.
Syria's army and Lebanese, Iranian and Iraqi loyalists re-entered Albu Kamal two days ago and by Saturday had taken most of it from IS, said the Syrian Observatory for Human Rights.
"Syrian regime forces, (Lebanese) Hezbollah, the Iranian Revolutionary Guard, and Iraqi militias seized control on Saturday of more than 80 percent of Albu Kamal, after a huge attack that began Friday night," said Observatory chief Rami Abdel Rahman.
"IS was pushed back to the northern and northeastern sectors of the city. Clashes are ongoing," Abdel Rahman told AFP.
The Britain-based monitor said the fresh push came with heavy bombing raids by regime ally Russia, and that troops were advancing more "carefully" than in their previous assault to ensure their gains would not be rolled back.
A string of territorial defeats across northern and eastern Syria left Albu Kamal, near the border with Iraq, as the last significant town held by IS in the country.
Losing it to regime forces would cap the group's reversion to a guerrilla organisation with no urban base.
On Saturday, Syrian state television aired live footage from Albu Kamal, showing plumes of smoke rising over the city's skyline as explosions echoed in the background.
It said the army was preparing to "storm the remaining areas" held by IS in Albu Kamal's east.
"What has most impeded the Syrian army's advance is the large amounts of mines left by Daesh (IS) and its attempt at using families as human shields," state television reported.