Police in Australia have arrested a man they believe to be responsible for planting twenty-seven letter bombs in the past two days.

A nationwide alert had been issued after a large number of them were discovered at a mail centre in the federal capital, Canberra.

Police also had to evacuate a train because of a suspected bomb.

Most of the letter bombs were addressed to tax office staff, and police say the man is believed to hold a grudge after losing his job in the taxation department.

The Australian prime minister John Howard said the campaign was a reminder that urban terrorism was a reality.