Foreign Minister Mohammad Javad Zarif levelled the accusations despite an expanding US air campaign in Iraq since August 8 that provided key support in relieving a jihadist siege of a Shiite Turkmen town north of Baghdad late last month.
Iran and the US have a shared opposition to IS, which controls a swathe of both Iraq and neighbouring Syria, but both governments deny cooperating militarily against the jihadists.
"There is still no serious understanding about the threat and they (the US) have as yet taken no serious action," Zarif was quoted as saying by Iran's Mehr news agency.
Iran has been Assad's main ally since a revolt against his rule erupted in 2011, rapidly spiralling into a civil war in which at least 191,000 people have been killed, according to the United Nations.
Shiite Iran has also provided military advisers to the Shiite-led government in Baghdad to assist its efforts to win back territory north and west of the capital that it lost to a lightning offensive spearheaded by the jihadists in June.
Although Tehran and Washington have denied cooperation in Iraq, State Department spokeswoman Marie Harf said Friday that the US was "open to engaging" with Iran, as it has on select issues in the past, notably on Afghanistan in late 2001.
"But we will not be coordinating our action together," she added.
Despite his criticism of Washington, Zarif said Tehran believed in the need for international cooperation to tackle the IS threat.
"This danger threatens the entire region and requires international cooperation.
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
