China's largest bank, the Industrial and Commercial Bank of China, has sold a stake worth 18.03 billion yuan (2.25 billion dollars) to the nation's social security fund.

The strategic investment agreement was signed with the National Social Security Fund in Beijing Monday but requires approval from the country's regulator, the lender said in a statement.

No details of the size of the stake were provided.

The social security fund has also bought into Bank of China, which listed in Hong Kong this month, and the Bank of Communications, which was the nation's first large bank to list in the former British colony last year.

Industrial and Commercial Bank is planning an initial public offering (IPO) in Hong Kong this year that could see the lender raise over 80 billion yuan (9.95 billion dollars), according to previous state press reports.

In January it sold a 10 percent stake for 3.78 billion dollars to a foreign consortium led by Goldman Sachs, American Express and Allianz.

The national security fund was set up as part of China's ongoing reform programme to help finance social welfare services, mainly pensions.