Regime forces backed by Russia, and Iranian militias capture 13 villages and small towns in Aleppo province, a war monitor says. Separately, car blast targets civilians in northern Tal Abyad town.
Syrian regime forces on Sunday seized a dozen villages and small towns as they pressed an offensive in the country's northwest against the last major rebel and opposition bastion, a war monitor said.
They captured 13 villages and small towns north and northwest of the city of Aleppo, the Britain-based Syrian Observatory for Human Rights (SOHR) said.
On Sunday, Russian warplanes mounted heavy air strikes in the Aleppo province, bombing towns including Anadan, which was later seized by Syrian regime forces supported by Iranian-backed militias, activists reported.
Rebel military sources said opposition fighters had pulled back from the area, including Anadan and the town of Haritan.
"In day one, they took an area where for eight years they could not take a single village," Rami Abdulrahman, director of the UK-based SOHR said.
"There is very rapid advance by the (Syrian) regime in this area," Abdulrahman said.
"The factions have withdrawn from most of the area," he added. The Observatory said Syrian regime forces had seized 13 towns and villages in the area.
Backed by Russian air strikes, regime forces have kept up the assault on the Idlib region and areas of neighbouring Aleppo and Latakia provinces since December.
Syria's regime-run agency SANA said army units were pushing on with their advance around Aleppo.
Regime forces have for weeks been making gains in northwestern Syria and chipping away at territory held by the opposition and rebel groups, focusing their latest operations on the west of Aleppo province.
The drive aims to bolster grip on Syria's second largest city Aleppo, which the Syrian regime retook completely from opposition groups at the end of 2016 but which is still targeted by rocket fire.
Last week, regime forces seized control of the strategic M5 highway which connects the capital Damascus to Aleppo, the country's former economic hub, and is economically vital for the Bashar al Assad regime.
According to the Observatory, Assad's forces are trying to consolidate a "security belt" around the M5 and on Friday they seized a key base lost to the rebels in 2012 just west of Aleppo.
The Russian-backed offensive has triggered the largest wave of displacement in Syria's nine-year conflict, with 800,000 people fleeing since December, according to the United Nations.
More than 400,000 people have been killed in Syria since the conflict broke out nearly nine years ago with a brutal crackdown on anti-regime protests. More than half of the country's population has been displaced in the war.
Bomb attack kills four civilians
At least four civilians were killed in a bomb attack in northern Syria, a security source told Anadolu Agency on Sunday.
According to initial reports, the attack was carried out using a bomb-laden truck in Tal Abyad district, said the source, who asked not to be named due to the restrictions on talking to the media.
Tal Abyad was cleared of terrorists in October by Turkey's anti-terror Operation Peace Spring, launched to eliminate YPG/PKK terrorists from east of the Euphrates River to secure Turkey's borders, aid in the safe return of Syrian refugees, and ensure Syria's territorial integrity.