The Britain-based Syrian Observatory for Human Rights said 38 members of government forces were killed in Thursday's blast, which brought down a building used by the regime in Aleppo's Old City.
The monitor had earlier reported a toll of 14.
A video posted online by the Thuwwar al-Sham rebel group purported to show the incident, with members of the force walking though a long tunnel and preparing barrels full of explosives.
"We are now inside the tunnel that will be detonated soon, God willing, the tunnel under the traffic branch building, which is an important headquarters for the Assad regime and its mercenaries," a rebel says in the video.
A huge geyser of dirt and smoke shoots upwards from the scene of the blast, after which gunfire can be heard.
Aleppo was once Syria's economic powerhouse, but it has been ravaged by the conflict that began in March 2011.
The city has been roughly divided between government control in the west and rebel control in the east since shortly after fighting began there in mid-2012.
The east of the city has been under siege for the past two weeks, since government forces severed the only remaining supply route into rebel-held districts.
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
