London transport officials blocked an advertising campaign suggesting gay people can be converted to heterosexuality.

The advertisements from Christian group Core Issues Trusts, which advocates "reparative therapy" to turn homosexuals straight, were slated to run for two weeks starting Monday on buses serving five routes in London.

Bearing the message "Not gay! Post-gay, ex-gay and proud. Get over it," the advertisements appeared to mimic a recent ad campaign from gay equality group Stonewall that read "Some people are gay. Get over it."

London Mayor Boris Johnson, who chairs Transport for London, ordered that the advertisements booked by Core Issues be pulled amid public outcry over the campaign.

"London is one of the most tolerant cities in the world and intolerant of intolerance," Johnson said Thursday. "It is clearly offensive to suggest being gay is an illness someone recovers from and I am not prepared to have that suggestion driven around London on our buses."

Stonewall spokesman Andy Wasley welcomed the decision, saying the group is "delighted" by Transport for London's commitment to diversity.

But Core Issues' co-director Mike Davidson criticized the move as censorship and said his group had gone through the proper channels to book the ads.

"It is of deep concern that there can only be one point of view and that is the point of view of individuals who are determined to push through gay marriage and apparently believe that homosexuality cannot be altered in any possible way," he said. "This is a disturbing development."

The advertising campaign was also backed by Christian group Anglican Mainstream and cleared by industry regulator the Advertising Standards Authority.

Core Issues' website says the organization is "a non-profit Christian initiative seeking to support men and women with homosexual issues who voluntarily seek change in sexual preference and expression."

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Cassandra Vinograd can be reached at http://twitter.com/CassVinograd