Thai stocks ended near a four-week low on Monday after four straight days on the retreat as a fresh outbreak of Sars in China weighed on overall investor sentiment, analysts said.
Bargain hunters took profits in industrial conglomerate Siam Cement which had been boosted by expectations it would post its best quarter ever on surging Chinese demand for petrochemicals products.
Shares in Siam Cement, which will announce its first quarter earnings on Wednesday, dipped 2.6 percent to 222 baht.
"There was more negative news than positive news in the market and investors opted to take quick profit in Siam Cement ahead of earnings results," said Sittiporn Jennaimuang, assistant vice president of research at UOB Securities.
The benchmark Stock Exchange of Thailand (SET) composite index ended down 14.27 points, or 2.09 percent, at 667.61, its lowest close since March 31.
The big-cap SET 50 index slipped 2.24 percent to 45.02 points and turnover fell to 15.7 billion baht ($395.9 million) from 19.4 billion baht on Friday.
They attributed the market falls to concerns about a Sars outbreak and a bomb threat.
"The market was pressured by regional factors due to a fresh Sars outbreak in China. Investors were also cautious after a report about a bomb threat," said Pichai Lertsupongkit, vice president of research at KGI Securities.
The offices of Korean Air in Bangkok said on Sunday they had received a bomb threat targeting flights between Thailand and Seoul.
Worries over the fresh Sars outbreak in mainland China sent Asia stock markets lower, with Hong Kong stocks and South Korea shares both down.
Investors cashed out financial stocks after last week's quarterly earnings announcements, with number two bank Krung Thai Bank, the sixth active trade, down 4.5 percent at 10.6 baht, sending the banking stock index 2.6 percent lower.
Shares in National Petrochemical were down 0.5 percent at 96.5 baht although the company said it expected first-quarter earnings to rise by at least 20 percent due to higher olefins prices.
On the rise were shares in Bank of Asia, which gained 3.9 percent to 5.4 baht after the Netherlands' ABN Amro picked Singapore's United Overseas Bank Ltd as the winning bidder to buy its 80.77 percent stake in the bank.
Shares in contractor Sino-Thai Engineering and Construction were up 1.33 percent at 15.2 baht, retreating from last week's fall of more than 20 percent on concerns the firm's first quarter profit would be hurt by higher materials prices.