BANGKOK (Bloomberg) — Thailand's rating outlook was downgraded to "negative" by Moody's Investors Service after months of political protests culminated in an airport siege and the ouster of Prime Minister Somchai Wongsawat in the past week.

"The rating action has been prompted by the adverse effects that the current heightened political uncertainty are having on the Thai economy, which could undermine the government"s creditworthiness if not checked," Moody's said in a statement today.

Moody's, which joined Fitch Ratings and Standard & Poor's Ratings Services in cutting the outlook this week, rates Thailand's foreign- and local currency government ratings Baa1, three levels above non-investment grade. Both Fitch and Standard & Poor's have BBB+ ratings for the country's debt, a level similar to Moody's.

Anti-government demonstrators in Thailand seized airports and took over the prime minister's office in a 192-day campaign that ended on Tuesday against allies of former Prime Minister Thaksin Shinawatra, whom they accused of trying to turn the country into a republic. The government said this week Southeast Asia's second-largest economy may not expand next year amid the political turmoil and a global recession.

"The political uncertainty is likely to continue," said Julia Goh, an economist at CIMB Investment Bank Bhd. in Kuala Lumpur. The downgrade in the outlook will "just dampen confidence further" and higher funding costs would deter companies from investing and expanding, she said.