The jihadists captured eight villages between second city Aleppo and the Turkish border, buoyed by their successes in neighbouring Iraq, the Syrian Observatory for Human Rights said.
They killed at least 40 fighters of rival rebel groups and captured at least 50 more for the loss of 12 of their own men, the Britain-based group said.
IS already controls almost all of the Euphrates valley provinces of Raqa and Deir Ezzor and has been making gains further west at the expense of rival rebel groups which it has been fighting since December.
The Observatory said the IS capture of the villages was a strategic prize, because it would open the way for the group to attack the towns of Marea and Azaz.
Marea is a stronghold of the Islamic Front, a coalition of Islamist groups that is among those fighting against IS.
Azaz sits next to the border crossing with Turkey, which would be a valuable asset to IS as it seeks to expand its self-declared "caliphate" in the territory it holds in Syria and neighbouring Iraq.
But its abuses against civilians and rival fighters, as well as its bid to dominate control of captured territory, sparked a backlash.
The group was pushed out of much of the territory it held in Aleppo province by the coalition of moderate and Islamist rebels that turned against it in January.
But it has been able to recapture some of that lost ground assisted by the decision of the Islamist Dawud Brigade to pledge allegiance to it.
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
