updated 8/16/2011 4:53:06 AM ET 2011-08-16T08:53:06

An investigation into the mysterious deaths of a U.S. woman and four other tourists in hotels in northern Thailand has suggested a link to toxic chemical exposure, but failed to determine exactly what killed them, according to a government website Tuesday.

  1. Don't miss these Travel stories
    1. Lords of the gourd compete for Punkin Chunkin honors

      With teams using more than 100 unique apparatuses to launch globular projectiles a half-mile or more, the 27th annual World Championship Punkin Chunkin event is our pick as November’s Weird Festival of the Month.

    2. Airports, airlines work hard to return your lost items
    3. Expert: Tourist hordes threaten Sistine Chapel's art
    4. MGM Grand wants Las Vegas guests to Stay Well
    5. Report: Airlines collecting $36.1B in fees this year

The victims — from New Zealand, France, and Britain as well as the U.S. — were staying at three different hotels in the popular northern Thai city of Chiang Mai.

A Thai tour guide also died, and three other tourists fell ill but recovered.

No one has been declared responsible in the spate of deaths, which came in January and February.

"The specific agents that caused the deaths and illnesses in these events cannot be identified, and it can not be determined exactly how people were exposed to them," the Department of Disease Control said on its website Tuesday.

The results were most revealing concerning a 23-year-old New Zealand woman who died Feb. 6, her two females companions — both also 23 — who got sick but recovered, and a 47-year-old Thai woman who died February 3.

The four are "most likely to have the same cause of illness, probably exposure to some toxic chemical, pesticides or gas," the report states.

The deaths of a British couple in their 70s found in their hotel room Feb. 19 were "possibly related" to the those deaths "as they occurred in the same hotel," the report states.

'Chemical or biotoxin'
Those deaths happened at the Downtown Inn in Chiang Mai. The hotel owner declined to comment Tuesday.

  1. Only on NBCNews.com
    1. OWN via Getty Images
      From belief to betrayal: How America fell for Armstrong
    2. pool via Reuters file
      US to Syria neighbors: Be ready to act on WMDs
    3. China: One-child policy is here to stay
    4. NRA: Practice Range
      New 'Practice Range' shooter game says it’s from NRA
    5. 'Gifted' priest indicted in crystal meth case
    6. AFP - Getty Images
      China's state media admits to air pollution crisis
    7. AFP - Getty Images
      French to send 1,000 more troops to Mali

In the case of the 33-year-old American woman who died January 11 "the suspected agent that caused her death is likely to be chemical or biotoxin in nature and it is probable that it might have been a pesticide," the report states.

She was staying in a different hotel in the same area and a 29-year-old Canadian woman traveling with her fell ill but recovered.

The final death, a 25-year-old French woman who died January 19, the report starts "developed fever and other symptoms on 16 January before arriving in Chiang Mai" so her case is probably not related to the others.

The website added authorities are taking measures to reduce the risks to visitors, but it did not give details.

Copyright 2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Discuss:

Discussion comments

,

Most active discussions

  1. votes comments
  2. votes comments
  3. votes comments
  4. votes comments