Hezbollah fighters took control Thursday over the valley and crossing point of al-Darb, southwest Arsal, as well as over checkpoint set by al-Nusra Front members in the region of al-Rahweh.
The Shiite party fighters are currently advancing towards the plain of al-Rahwe.
On Wednesday, the Lebanese group said in a statement its fighters had seized three hilltops in the mountainous area east of the Lebanese town of Arsal, the target of an incursion last August by the al Qaeda-linked Nusra Front and Islamic State.
Hezbollah's support has been crucial to Syria's President Bashar al-Assad in the four-year-long Syrian conflict. Its operation in the Qalamoun mountains north of Damascus is part of Assad's effort to shore up his control over western Syria.
Assad has lost swathes of northwestern and eastern Syria in the last two months to an array of insurgent groups including both the Nusra Front and Islamic State, putting him under the toughest military pressure he has faced since the war began.
LBCI/REUTERS