Kosovo police seized four kilos of heroin in Prizren, southern Kosovo, on Monday, and arrested four ethnic Albanians in connection with the incident, DPA reported. "The search operation was conducted in Prizren's Bajram Curri neighbourhood. Some anti-drug police units, assisted by German KFOR troops, raided three different houses," Kosovo police spokeswoman Sabrie Kamberi told Deutsche Presse-Agentur, dpa. During the operation, an unspecified amount of explosives were also discovered. With its porous borders and undefined status -- it is administered by the United Nations-- Kosovo is believed to be one of the main portals for drug smuggling from the Middle East and neighbouring Albania to West European countries.