The crisis facing pension plans for US state and municipal employees is deepening as investment losses deplete the resources of retirement funds for teachers, police officers, firefighters and other local government workers.

The largest state and municipal pension plans lost 9 per cent of their value in the first two months of this year, according to data from Northern Trust. That followed a loss of 26 per cent in 2008. Smaller funds, which underperform the larger ones, lost more, experts say.