COPENHAGEN -- Police were on heightened alert in Scandinavian countries Tuesday over several suspicious letters and the discovery of white powder in a bus that triggered fears of anthrax poisoning.

In Denmark, several incidents of individuals or companies receiving suspicious looking letters have been reported to police since Monday.

A police official said Tuesday, that a bus in Copenhagen had to be evacuated and quarantined after some white powder was discovered inside it.

Both the bus and the letters are now being examined by scientific experts at the Copenhagen Institute of Serology.

A pensioner in the northern town of Aalborg and two social workers visiting him were given precautionary treatment for anthrax poisoning after touching a letter containing a white substance which arrived from South Korea.

According to the Copenhagen institute, the majority of the letters analyzed so far, several of which had Italian postmarks, did not contain any poisonous substances, the rest are still under examination.

Alarm was also raised in the Danish territory of Greenland after a member of the local government opened a mysterious letter from the United States.

The letter which was immediately resealed is now being examined in Copenhagen.

In Sweden, four suspicious letters were handed into police Monday and are now being analyzed by army scientists, according to Swedish News Agency THU.

While in Norway local government officials handed over several suspect letters to police for analysis.

Thirteen people have so far been exposed to the deadly anthrax bacterium in the United States. One has died of the disease and another four have contracted it.

U.S. authorities are not ruling out a link with extremist supporters of Osaka bin Laden, wanted in connection with the devastating September 11 suicide jet attacks in New York and Washington.