Three New Zealand soldiers have been killed by a roadside bomb in central Afghanistan.

The soldiers were travelling in a vehicle on Sunday in Bamiyan province, a once comparatively stable part of the country where there has recently been an increase in violence. Two New Zealand soldiers were killed in the same area during a firefight with insurgents earlier this month.

New Zealand has stationed a small group of 145 soldiers in Afghanistan since 2003, a contingent it plans to withdraw by the end of next year. Ten New Zealand soldiers have now died during the conflict.

John Key, New Zealand's prime minister, said that the deaths "underscore the gravity" of the situation the soldiers face in Afghanistan each day, adding that he would release further details of the incident later on Monday.