All Southeast Asia markets fell on Monday over debt worries in the euro zone, while Thai stocks slipped to a one-month low after at least 37 people were killed in violent protests in Bangkok.
Thailand .SETI fell 2 percent, Singapore .FTSTI slid 0.75 percent to a one-week low, and Indonesia .JKSE closed 1.4 percent weaker.
Malaysia .KLSE shed 0.4 percent, the Philippines .PSI lost 1.2 percent and Vietnam closed 1.8 percent lower.
Analysts said concerns over euro zone debt crisis triggered the fall after the U.S. stocks fell on Friday investor on concerns over the sustainability of European public debt, despite a $1 trillion bailout package announced last week.
"Until something is clear over these worries like strong emergence of recovery, the trend will continue," said Song Seng Wun, a regional economist at CIMB-GK Research in Singapore.
"At this juncture, investors know are more concerned of possible risk coming up from China and Europe and they are taking much more short term view."
German Chancellor Angela Merkel said on Sunday that a $1 trillion EU rescue plan had only bought the euro zone time to tackle its fundamental problem -- a yawning gap between its strongest and weakest economies.
In addition to euro zone woes, political violence in Bangkok that killed at least 37 people since Thursday, sent the SET index to its lowest since April 20. The government on Monday demanded an end to protests before holding talks with opponents seeking immediate elections.
The market fell more than 3.1 percent in early trade, but recouped some losses as investors priced in the unrest.
"Sentiment was dampened by external and domestic factors," said Teerawut Kanniphakul, senior analyst at CIMB Thai Securities. "Due to political unrest, the index should fall further but it should not breach the previous low of 720 points."
Top energy firm PTT PTT.BK fell 2.4 percent and Siam Commercial Bank SCB.BK lost 3.6 percent.
In Singapore, Oversea Chinese Banking Corp (OCBC.SI) fell 0.1 percent and the country's biggest telephone firm Singapore Telecom (STEL.SI) slid 1.7 percent.
Jakarta, the best performing Southeast Asian market so far this year, fell led by mines shares with 5 percent fall in top minor Bumi Resources (BUMI.JK).
Malaysia .KLSE was off 0.4 percent with planter IOI Corp. (IOIB.KL) and telecoms firm Axiata Group (AXIA.KL) falling over 1.8 percent.
Manila, which hit a 16-month high the previous session, fell due to a technical correction along with the euro zone debt worries, analysts said. It climbed 6 percent last week amid optimism after the country's presidential election.
Among losers on Monday, Ayala Land (ALI.PS) lost 5.2 percent and Energy Development Corp. (EDC.PS) fell 3.8 percent.
In Hanoi, 3.1 percent fall in Vietcom Bank VIC.HM and 4.7 percent slip in PVFC PVF.HM drove the index 1.8 percent down to its lowest since April 2.
