Nippon Life Insurance Co. could increase its stake in Principal Financial Group Inc. after the Des Moines-based insurer said it may seek strategic investors to raise capital as market conditions continue to deteriorate, Bloomberg reported.

The Japanese insurer, which has a 7 percent stake in Principal already, may boost its investment to 15 percent, according to Nikkei English news, which did not say where it got the information. A person familiar with the matter confirmed to Bloomberg that Nippon was looking to increase its investment.

Nippon Life first invested in Principal in 2001 and raised its stake from 4.3 percent last February. It also has formed an alliance with Milwaukee-based Northwestern Mutual Life Insurance Co. as it moves to expand its asset-management and overseas businesses.

Principal said in a regulatory filling yesterday that it may look for strategic investors, which often signifies that a company may be interested in receiving bids for all or part of its business.

“Market conditions may limit our ability to replace, in a timely manner, maturing liabilities; satisfy statutory capital requirements; fund redemption requests on insurance and other financial products,” Principal said in the filing.

Principal’s stock price has plummeted 53 percent this year. In its filing yesterday, the company said it could also issue securities and cut expenses to ensure that its cash flow is sufficient for current liquidity needs. Principal already has halved its dividend, suspended share repurchases and cut jobs to conserve cash as losses and write-downs related to the subprime mortgage market totaled about $4.5 billion last year, according to Bloomberg data.

Iowa Insurance Commissioner Susan Voss also has loosened reserve requirements on the insurer, increasing the statutory surplus at Principal’s main life unit by about $387.4 million.

Principal has sought as much as $2 billion from the Treasury Department’s Troubled Asset Relief Program.