TOKYO (Reuters) - Japan's public pension fund, the world's largest, logged more than $50 billion in investment losses last fiscal year as the yen surged and Tokyo stocks fell amid global market turmoil, a person with direct knowledge of the matter said.

Portfolio losses for the Government Pension Investment Fund for the 12 months through March were between 5 trillion and 5.5 trillion yen, the person told Reuters on Friday, speaking on condition of anonymity as the results are not public.

The $1.4 trillion GPIF has taken a more aggressive investment stance in recent years, shifting towards stocks and away from low-yielding Japanese government bonds, in line with Prime Minister Shinzo Abe's push to deploy more of Japan's huge financial assets in riskier investments and boost economic activity.

The Nikkei stock average <.N225> fell 13 percent last fiscal year.

The GPIF plans to announce the fiscal-year results on July 29, the source said. That is later than the usual early-month timing - and after a July 10 national election.

(Reporting by Takaya Yamaguchi; Writing by William Mallard; Editing by Chris Gallagher)