The California Public Employees' Retirement System, the largest U.S. public pension fund, said it lost 2.4 per cent during the year ended June 30, as stock losses caused its worst performance in six years.

The performance of the fund, with $239 billion US in assets, compared with a 19 per cent gain in the previous fiscal year. Calpers, as the fund is known, said its stock portfolio lost 10.7 per cent.