Stung by a falling share price after an analyst expressed concern over its exposure to European bank hybrid debt securities, an Aflac Inc. (AFL) spokeswoman said Thursday the insurer is "comfortable with our current capital position and are constantly monitoring our investment portfolio."

She said the company will offer more "specific details" along with its earnings release Feb. 2.

Shares of Aflac Inc. dropped to their lowest level since mid-2000 Thursday after Morgan Stanley analyst Nigel Dally said in a research note that the insurer's exposure to hybrid securities issued by European banks, including Royal Bank of Scotland Group PLC (RBS), is a "rapidly escalating concern."

Aflac shares fell as much as 39% to $22.08 in morning trading after Dally told the firm's clients to avoid Aflac's stock owing to its $7.9 billion of exposure to securities that have been sharply marked down after European financial firms announced large losses this week.

Shares of Aflac recently traded down 31.1% to $24.95.

-By Ed Welsch, Dow Jones Newswires; 201-938-5244; edward.welsch@dowjones.com and Lavonne Kuykendall, Dow Jones Newswires; (312) 750 4141; lavonne.kuykendall@dowjones.com

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