Image copyright AP Image caption The Washington transit system has suspended all "issue-oriented" advertising

Transport officials in Washington DC have blocked plans by an American free speech pressure group to have a controversial cartoon of the Prophet Muhammad displayed on the subway.

The American Freedom Defense Initiative wanted to display the cartoon, which won first prize at an event in Texas.

Two gunmen were shot dead by police outside the event earlier this month.

Washington transport authorities on Thursday banned political, religious and advocacy adverts on the subway.

The transport authority in the US capital voted unanimously to suspend advertisements it describes as "issue-oriented".

Image copyright AFP Image caption Police blew up the car used by the Texas attackers shortly after they carried out their strike earlier this month

AFDI founder Pamela Geller strongly criticised the decision to ban the advert, describing it as an attack on free of speech.

Ms Geller commented 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."

The advert calls for Americans to support free speech and features a bearded, turban-wearing Muhammad waving a sword and shouting: "You can't draw me!"

In reply, a cartoon bubble portrays an artist grasping a pencil and saying: "That's why I draw you."

Ms Geller insists the cartoon is a "political opinion" which does not contain any violence.

Her organisation, described by critics as a hate group, has run controversial adverts on subways and buses in Chicago, Philadelphia and San Francisco as well as in Washington's Metro in 2012.

Image copyright Reuters Image caption Ms Geller is an outspoken critic of Islam

Pamela Geller: America's controversial blogger

A staunch critic of Islam since 2005, she rose to prominence in 2010 through her online opposition to Park 51, a planned Muslim community centre in Lower Manhattan close to the World Trade Center site

Heads the American Freedom Defense Initiative (AFDI), which has also caused controversy by buying advertising space on buses in US cities, criticising Islam

The 56-year-old describes herself online as a free-speech activist, but her critics denounce her as a "bigot"

She insists the focus of her criticism is chiefly against radical Islam, but has been quoted as saying that "Islam is the most anti-semitic, genocidal ideology in the world"

Speaking of her role in organising the Muhammad Art Exhibit in Garland, she said: "We draw Muhammad because we are free... We draw Muhammad because our unalienable rights are enshrined in the First Amendment."

Pamela Geller: America's 'bigoted blogger'