Japan's Dai-ichi Life Insurance Co has agreed to buy U.S. peer Protective Life for $5.7 billion, the largest acquisition by a Japanese insurer, displaying its determination to grow overseas to counter weak prospects at home.

Dai-ichi Life, Japan's second-largest private-sector life insurer, said it will issue up to 250 billion yen ($2.4 billion) in new shares to help finance the widely expected purchase of Protective Life. The Japanese insurer will retain existing management at the Birmingham, Alabama-based target, which booked premiums and policy fees of $2.98 billion and net income of $393 million in 2013.

Faced with weak growth prospects at home amid Japan's ageing population, Dai-ichi Life and other Japanese insurers have been buying assets in more dynamic markets from the United States to Southeast Asia. While the U.S. insurance market is the world's biggest, demand for insurance policies in Southeast Asia is expected to rise among the region's emerging middle class.

Under terms of the deal, Dai-ichi Life will pay $70 per share to buy 100 percent of Protective Life, a 35 percent premium to Protective's average share price in the past month. The Japanese company said it expects the deal to close sometime between December 2014 and January 2015, pending approval by the target's shareholders and regulators.

Ranked 36th among U.S. insurers by premium income, Protective Life will provide Dai-ichi Life with a growth platform in North America, the Japanese company said in a statement.

Dai-ichi Life has a precedent for deals in overseas markets boosting its performance. It bought out Tower Australia Group Ltd for $1.2 billion in 2010, and thanks to strong growth at the Australian unit, Dai-ichi Life was the only major life insurer to book an increase in premium revenues for the year ended in March 2014.

In a deal more typical of the investments made by Japanese insurers in Southeast Asia, last month Japan's largest private-sector life insurer, Nippon Life Insurance Co [NPNLI.UL], agreed to buy 20 percent of Indonesia's Sequis Life for 4.87 trillion rupiah ($413 million).

Dai-ichi Life said it will issue new shares to raise up to 250 billion yen to help finance the acquisition, but has enough funds on hand to cover the rest.

According to its shelf registration, it may issue new shares any time during a one-year window opening on June 12. The company said Goldman Sachs and Nomura will be main underwriters.

Goldman Sachs is financial advisor to Dai-ichi Life and Baker & McKenzie and Willkie, Farr & Gallagher are acting as legal advisors. Morgan Stanley is serving as financial advisor to Protective Life and Debevoise & Plimpton LLP is serving as legal advisor, the companies said in the statements.

Dai-ichi Life shares ended up 3.6 percent at 1,499 yen on Wednesday, outperforming a 0.2 percent gain in the benchmark Nikkei average.

($1 = 102.4300 Japanese Yen)

($1 = 11784.0000 Rupiahs)