Cigna Inc., the world’s largest provider of employer-purchased medical insurance for expatriates, moved today into the Singapore health-plan market, expanding its global coverage to 28 countries.

The Philadelphia-based insurer was granted a license to operate in Singapore to sell insurance and will market health and dental plans to the estimated 7,000 multinational employers with operations there, said Andrew Kielty, president of Cigna International’s expatriate benefits unit. The Ministry of Manpower in Singapore reported that as many as 110,000 expatriates work in the island nation.

Singapore was the missing piece for Cigna in “a powerful triangle of decision-making” in Asia that includes Hong Kong and Shanghai, Kielty said in a telephone interview. Cigna’s international business accounted for about 19% of adjusted earnings in 2010, the company said in an e-mail.

“This places us in a unique position among insurers, and the job of expansion in Asia is far from done,” Kielty said. “We have a list of other places worthy of exploration.”

Cigna has led US-based insurers in developing international markets, with only Aetna Inc. expanding to China in recent years, said Dave Shove, a New York-based analyst at Bank of Montreal.

Cigna and Aetna have concluded “the US health-benefits market is pretty mature and doesn’t present the opportunities it used to,” Shove said. “Cigna has a big head start internationally, there’s no doubt.”