Norway's sovereign wealth fund, the world's biggest, will from now on vote against the nomination of all-male boards in Japanese companies, a senior fund official said Tuesday.

In a bid to promote diversity and gender equality, the fund, currently worth more than 15 trillion kroner ($1.34 trillion), already rejects nominations to boards for companies in Europe and North America that do not include at least two women.

Japan, where the business world has long been very male-dominated, had been given a grace period.