Thai stocks led other Southeast Asian equities ended lower on Monday on growing fears over escalating US-Iran tensions, which led to a spike in oil prices and a decrease in risk appetite of investors.
US President Donald Trump on Sunday warned of "major retaliation" if Iran strikes back for the killing of its military commander Qassem Soleimani last week.
Oil prices rose a further 2% on Monday, pushing Brent above $70 a barrel, after Trump on Sunday threatened to impose sanctions on Iraq after its parliament passed a resolution calling for an end to all foreign troop presence.
"A severe escalation of tensions in the Middle East, or even outright hostilities, has the potential to easily subsume any benefits gained from the interim US-China trade agreement," Jeffrey Halley, an analyst at OANDA, said in a note.
"The price actions of Friday and this morning (Monday) suggest that early casualties will be emerging markets and regional Asia," he added, highlighting Asia's dependence on oil imports.
Thai stocks led the declines in the region, ending 1.7% lower, with Kasikornbank Plc and Siam Cement Plc among the top drags, losing 5.9% and 3.6%, respectively.
Financials weighed on the Indonesian equities, with Bank Central Asia and Bank Mega Tbk shedding 1% and 10.2%, respectively.
Financials and consumer firms were among the top losers on Malaysia's benchmark index, which fell 0.9%. Heavyweights Malayan Banking and Sime Darby Plantation shed 1.1% and 2.2%, respectively.
Singapore's benchmark index slipped the most in over six weeks. Heavyweights DBS Group Holdings and Jardine Strategic Holdings shed 0.5% and 0.9% each.
The Philippine bourse trimmed its losses to finish 0.5% lower, with property developer SM Prime Holdings and consumer food firm Universal Robina Corp losing 1.4% and 1%.
President Rodrigo Duterte signed a 4.1 trillion peso (2.4 trillion baht) budget for this year, up 12% from last year, to ensure timely funding for an infrastructure overhaul in the country. The Vietnamese index fell most in over one month, with financials and real estate stocks being the top losers.