Rio de Janeiro  - Young foreign tourists who travelled to Brazil for the world-famous Rio de Janeiro Carnival were facing an unexpected threat Thursday: the raids of criminal gangs on youth hostels in the city.

In just 24 hours, police investigated two such raids, affecting at least 50 tourists, most of them foreigners.

In the early hours of Thursday, seven armed men went into a hostel in the Bohemian central Rio neighbourhood of Lapa. According to preliminary investigation, at least 34 guests - from the United States, Britain and South Korea - were robbed of cash, cameras and passports.

The attack happened some 24 hours after another group carrying guns and even grenades raided another hostel in the Copacabana neighbourhood. They stole property from at least 13 tourists, including one Colombian and 11 Israelis.

The formal stage of the Rio Carnival runs from Saturday to Tuesday. (dpa)