The assault in Raqa province, the jihadists' Euphrates valley stronghold, came amid their fiercest assault yet on Damascus-held territory.
The deaths added to 74 already killed in the offensive across the north and northeast, the Syrian Observatory for Human Rights said.
"At least 50 soldiers were ambushed, some of them were killed in fighting but most of them were beheaded," Observatory director Rami Abdel Rahman told AFP.
IS militants claimed the toll was as high as 75.
Media close to the regime remained silent on the deaths in Raqa.
The 17th division is one of three still holding positions in the IS-occupied region and operates out of a vast military base.
The army repositioned the 17th division yesterday, the Observatory said, without giving further details.
It is the first stand-off of this magnitude between IS and Syrian government forces, with the jihadists intent on "cleansing" the territories it controls of the regime presence, the Observatory said.
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
