ACE Ltd has agreed to buy a 60.9 percent stake in Thailand's Siam Commercial Samaggi Insurance PCL for about $185 million as foreign insurers step up their presence in underdeveloped Southeast Asian insurance markets.

Bangkok-based Siam Commercial Samaggi is an autos, small commercial, personal accident insurer and distributes its products through both Siam Commercial Bank branches and independent agents. It had about $138 million in gross premiums written in 2012.

Shares in Siam Commercial Samaggi were up 13 percent on Monday, while the benchmark Thailand stock index was down 0.2 percent. Siam Commercial Bank owns 24 percent of Siam Commercial Samaggi, according to Thomson Reuters data.

The deal comes despite the ongoing political unrest in Thailand, which has weighed on Thailand's currency and its stock markets as anti-government forces are determined to oust Prime Minister Yingluck Shinawatra.

In 2013, Thailand was Asia-Pacific's sixth-busiest M&A market, with $15.3 billion worth of deals, according to Thomson Reuters data.

Southeast Asia has been active market for bank and insurance deal making last year. Last year, Mitsubishi UFJ Financial Group (MUFG) agreed to buy 72 percent of Thailand's Bank of Ayudhya Pcl for $5.31 billion and Meiji Yasua Life Insurance Co agreed to pay about $700 million to buy a 15 percent stake in unlisted Thai Life Insurance Co.

Barclays plc and Siam Commercial Bank's investment banking unit was the sell side adviser, while Citigroup advised ACE, a person familiar with the matter said.

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