AMSTERDAM (AP) — Health authorities in Amsterdam are warning of dangerous drugs being sold to tourists after three British men died in the past 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. Similar signs were set up at other popular tourist haunts in the historic city.

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 probably bought believing it was cocaine.

Amsterdam police spokesman Rob van der Veen said the same drug is suspected in another British tourist's death last month. A further 14 people have become sick after taking the drug, Van der Veen added.

He said it is not yet clear why heroin is apparently being sold as cocaine. A team of police is investigating the case and trying to track down the dealer involved.

Tourists flock to Amsterdam to smoke marijuana at the city's famed "coffee shops," but liberal Dutch drug policies that allow pot smoking do not extend to hard drugs like cocaine and heroin, which remain illegal.

Even so, Van der Veen said tourists need not fear arrest if they call police and ambulance personnel after seeing somebody fall ill from taking drugs.

"If people are stupid enough to use and get sick we are not there to arrest them, we are there to save lives. That is our highest priority," Van der Veen said.

"If you get into problems, dial 112," he added, giving the Dutch emergency phone number.