BANGKOK, Thailand (AP) _ Scientists have discovered alarming levels of deadly cyanide in waters near some of Thailand's most popular beaches, a government official said Friday.

Environmental consultants also found smaller quantities of mercury, another toxin, while sampling the seabed next to an industrial complex at Rayong, a town 90 miles south of Bangkok.

They detected the chemicals during two tests made in preparation for the planned expansion of the Map Ta Phut port and industrial park, said Kasemsri Homchean, director of environmental safety for the government's Industrial Estate Authority.

Map Ta Phut lies at the western edge of a string of palm-lined beaches popular as a weekend retreat for Bangkok residents and foreign tourists.

Thailand's tropical beaches and islands are among its biggest attractions, and tourism is the country's most lucrative industry. At the same time, Thailand is building up its industrial base as fast as possible to keep up its high rate of economic growth.

The environment has often come out the loser.

The first test, made in September, found ``abnormally high'' concentrations of cyanide in sediment just offshore from the complex, Kasemsri said.

It showed cyanide in amounts as large as 4.5 parts per million, The Nation newspaper reported.

Kasemsri asked the consultants to do a second test. The results from samples taken in December showed about half as much cyanide but higher evidence of mercury.

``I asked them why the results are so different,'' she said. ``It makes no sense.''

Kasemsri said that neither toxin is likely to have originated from the petrochemical and steel factories operating at the coastal complex. She offered no other explanation.

``It's too early to conclude,'' she said, adding that she has ordered a third round of tests.

None of the scientists who found the chemicals could be reached for comment. They have stood by their findings and have yet to agree to perform a third test, Kasemsri said.

Discovery of the chemicals could impede plans to reclaim land needed to expand the port, The Nation reported. Dredges, for example, might churn up dangerous amounts of cyanide into the water.

Kasemsri played down this risk, saying the largest amounts of cyanide were discovered outside the area where dredging would occur.

Any decision to halt the project would have to be made by a government committee awaiting new test results, she said.

A tiny speck of cyanide can be deadly, but cyanide breaks down quickly in the presence of sunlight and oxygen. It does not accumulate in body tissues as some other poisons do. It is widely used to process gold and silver ore, and numerous spills have been reported at mining sites without reports of poisonings.