Bangkok - Thai shares lost 2.72 per cent of their value Monday on a combined whammy from heightening political instability and worldwide worries.

The Stock Exchange of Thailand (SET) index ended at 390.92, down 10.92 points or 2.72 perr cent.

"A combination of growing political instability in Thailand and falls on regional markets was dragging us down today," said Phuwadol Larpudomsuk, an analyst at Asia Plus Securities.

Thailand has been rocked by the seizure last week of Bangkok's two international airports by anti-government protestors, causing incalculable damage to the country's main engines of growth - exports and tourism.

Further instability is anticipated on Tuesday when the Constitutional Court is expected to pass a verdict disbanding the ruling People Power Party for election fraud, forcing Thai Prime Minister Somchai Wongsawat to resign.

Financial shares were the hardest hit on SET Monday, responding to Standard & Poor's Ratings Services announcement Monday that it had downgraded its outlook on Thailand's sovereign credit from stable to "negative," in response to Bangkok's two airports being closed down by anti-government protestors for almost a week.

"The recent occupation of the two airports in Bangkok by anti-government protestors has increased the risks to sovereign creditworthiness," said Standard & Poor's Singapore-based credit analyst Kim Eng Tan.

He added, "The sovereign ratings could be lowered if economic performance weakens sharply as a result, causing government finance to deteriorate seriously or banks' asset quality to worsen markedly." (dpa)