Thailand announced new measures on Tuesday to protect tourists after five foreigners died mysteriously in one city in just over a month, saying they were likely poisoned by unidentified toxic chemicals or pesticides as per agencies reports.

Two Britons, a Frenchman, an American and a New Zealander died between January 11 and February 19 this year in northern Chiang Mai, Thailand's second-biggest city. Three of the victims' traveling companions also fell ill.

The deaths drew negative media attention to a country that is one of the world's most popular tourist destinations, attracting some 14 million visitors a year to its beaches, mountains and sprawling capital, Bangkok.

Thailand's Department of Disease Control listed actions that will be taken to prevent more illness in Chiang Mai and other key destinations for tourism.

They included the close monitoring of the use of chemicals and pesticides in hotels, inspections of markets and street food vendors, health and safety training by local authorities, a review of investigation procedures and the setting-up of a website to advise tourists on potential health risks.

A five-month investigation led by the Thai authorities with cooperation from the World Health Organization and the U.S. Centers for Disease Control and Prevention was largely inconclusive but found no evidence of criminal cause.

Three cases were attributed to exposure to chemicals, pesticides or gas, while for two victims -- an elderly British couple -- there was no known cause.

Tourism is a vital part of Thailand's economy, Southeast Asia's second-biggest, employing about 15 percent of the country's workforce and contributing about 6 percent of GDP.