BARCELONA -- Adverts denying the existence of God began appearing on buses in Spain on Monday as part of a campaign inspired by a similar initiative that got underway earlier this month in Britain.

The ads on buses that service two routes in Barcelona, Spain's second-largest city, read: "There's probably no God. Stop worrying and enjoy your life" in Catalan.

They were paid for by the Catalan branch of Spain's Union for Atheists and Free Thinkers (UAL).

The same message was plastered on roughly 800 buses and in London's subway system several weeks ago, angering believers in Britain.

The Barcelona archbishop's office has already condemned the campaign, saying in a statement that "for believers, faith in God was not an obstacle to enjoying life, but 'a solid foundation to live life with an attitude of solidarity, peace and a sense of transcendence'.

"This campaign is not against believers, it is not even addressed to them. It is addressed to atheists, who are regularly threatened with punishments" in a country with a strong Catholic tradition, the president of the Catalan branch of UAL, Albert Riba, told AFP.

"We want to tell non-believers: 'Relax, God probably does not exist," he added.

The association wants to extend the campaign to the rest of the country, on buses in Madrid, Valencia on the Mediterranean coast, Bilbao in the northeast and Seville in the southwest.

It has so far collected 15,500 euros (21,000 US dollars) through its web site to finance the ad campaign.

In anticipation of the atheist advertising campaign, an evangelical pastor in Madrid has already paid for an opposing message to appear on a suburban bus route in Madrid that says: "Yes, God exists. Make the most of life with Christ."