The SET Index closed at 1,678.73 points, down 15.59 points, or 0.92 per cent, in the morning session on Tuesday with transactions totalling 8.16 billion baht.
Tisco Securities senior strategist Apichat Poobunjirdkul predicted the SET Index on Tuesday would fall, seeing the day's support level at between 1,670 and 1,680 and the resistance level at between 1,705 and 1,710.
He said Russia-Ukraine tensions intensified after Russian President Vladimir Putin ordered troops to station in Donetsk and Luhansk republics in eastern Ukraine. The move came after Putin's decision to recognise the independence of two breakaway regions.
Meanwhile, US President Joe Biden signed an executive order to bar Americans from trade and investment in Donetsk and Luhansk republics in response to Putin's move.
"However, the Thai stock market would not fall sharply as the index gained positive sentiment from over a 4-per-cent rise in oil price, due to Russia-Ukraine tensions," he said.
He also advised investors to follow the Centre for Covid-19 Situation Administration's meeting on Wednesday, to see whether additional measures to contain the spread of Covid-19 will be announced after the level 4 Covid-19 alert was sounded nationwide.