TOKYO (Reuters) - Japan's giant public pension fund, the world's largest, has issued a tender to hire asset management companies to supervise its US$101 billion (S$127 billion) portfolio of foreign bonds aimed at generating higher returns to cope with the country's ageing population.

The Government Pension Investment Fund (GPIF), which holds total assets of US$1.26 trillion and the scale larger than Mexico's economy, said on Wednesday that it will seek managers for emerging markets bonds, foreign high-yield, and foreign inflation linked bonds.

This is the first time the public fund will expand its foreign bond investment beyond conventional bonds.

Currently, GPIF only uses Citigroup's WBIG and WGBI indexes as benchmarks for its foreign bond investments.