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Amsterdam authorities warn of dangerous 'cocaine' after 3 British tourists die

  • An electronic sign post warns tourists of extremely dangerous cocaine being sold to tourists on Rembrandtplein square in the center of Amsterdam, Netherlands, Thursday, Nov. 27, 2014. Health authorities in Amsterdam are warning tourists after three British men died in the last month after snorting heroin they may have believed was cocaine. (AP Photo/Peter Dejong)

    An electronic sign post warns tourists of extremely dangerous cocaine being sold to tourists on Rembrandtplein square in the center of Amsterdam, Netherlands, Thursday, Nov. 27, 2014. Health authorities in Amsterdam are warning tourists after three British men died in the last month after snorting heroin they may have believed was cocaine. (AP Photo/Peter Dejong)  (The Associated Press)

  • A man takes a picture of Amsterdam's famous Bulldog coffeeshop where hashish and marijuana are legally sold as an electronic sign warns tourists of extremely dangerous cocaine being sold to tourist on Leiseplein square in the center of Amsterdam, Netherlands, Thursday, Nov. 27, 2014. Health authorities in Amsterdam are warning of dangerous drugs being sold to tourists after three British men died in the last month after snorting heroin they may have believed was cocaine. (AP Photo/Peter Dejong)

    A man takes a picture of Amsterdam's famous Bulldog coffeeshop where hashish and marijuana are legally sold as an electronic sign warns tourists of extremely dangerous cocaine being sold to tourist on Leiseplein square in the center of Amsterdam, Netherlands, Thursday, Nov. 27, 2014. Health authorities in Amsterdam are warning of dangerous drugs being sold to tourists after three British men died in the last month after snorting heroin they may have believed was cocaine. (AP Photo/Peter Dejong)  (The Associated Press)

  • A sign warns of extremely dangerous cocaine being sold to tourists as the belltower of the Oude Kerk, or Old Church, is seen outside Central Station in Amsterdam, Netherlands, Thursday, Nov. 27, 2014. Health authorities in Amsterdam are warning of dangerous drugs being sold to tourists after three British men died in the last month after snorting heroin they may have believed was cocaine. (AP Photo/Peter Dejong)

    A sign warns of extremely dangerous cocaine being sold to tourists as the belltower of the Oude Kerk, or Old Church, is seen outside Central Station in Amsterdam, Netherlands, Thursday, Nov. 27, 2014. Health authorities in Amsterdam are warning of dangerous drugs being sold to tourists after three British men died in the last month after snorting heroin they may have believed was cocaine. (AP Photo/Peter Dejong)  (The Associated Press)

Health authorities in Amsterdam are warning of dangerous drugs being sold to tourists after three British men died in the last month after snorting heroin they may have believed was cocaine.

A large sign outside the Dutch capital's Central Station warned Thursday, "Extremely dangerous cocaine is sold to tourists" in the area.

The warning campaign was started after two British men, aged 20 and 21, were found dead in a hotel room in the city on Tuesday. Police say they likely died after snorting "white heroin" they likely bought believing it was cocaine.

Amsterdam police spokesman Rob van der Veen says the same drug is suspected in another British tourist's death last month.

Van der Veen says it is not yet clear why heroin is apparently being sold as cocaine.