The winning entry from a Prophet Muhammad cartoon contest will not be allowed to be advertised on Washington's public transportation system, officials said.
The cartoon was part of a contest that came under attack in Texas last month, when two suspected Islamist gunmen opened fire on event participants with assault rifles, before a traffic policeman shot them dead.
The competition was staged by an anti-Muslim group, founded by Pamela Geller, who criticised the decision to ban the ads in the US capital, calling it an attack on free speech.
"This is an end run around the First Amendment," Ms Gellar said on her website.
She had submitted an advert featuring the winning entry to the Washington Metropolitan Area Transit Authority for review, but on the agency yesterday suspended "all issue-oriented" ads until the end of the year, The Washington Post reported.
The WMATA did not respond to a request for comment.
With a banner reading "Support free speech," the ad would have featured the winning cartoon, which showed a sword-wielding Prophet Muhammad saying: "You can't draw me."
The cartoonist replies in a voice bubble: "That's why I draw you."
Ms Geller said on her website that "rewarding terror with submission is defeat. Absolute and complete defeat."
"These cowards may claim that they are making people safer, but I submit to you the opposite. They are making it far more dangerous for Americans everywhere," she said.
Ms Geller is the president of the American Freedom Defense Initiative, which has been listed as an anti-Muslim hate group by US civil rights watchdog the Southern Poverty Law Center.
