Six Afghan soldiers have been killed as their post came under fire from NATO aircraft in the central province of Ghazni. Police described the bombing as friendly fire and said the army post was hit by mistake.A spokesman for the Afghan Defence ministry condemned the incident, saying it was not the first time Afghan soldiers had died in friendly fire. Gen Mohammad Zahir Azimi said the soldiers had been launching an attack against insurgents in Ghazni province in eastern Afghanistan. Meanwhile, Nato confirmed the airstrike had gone wrong and said it regretted the deaths. Spokesman Brig-Gen Josef Blotz said a joint investigation had been launched. The incident comes as international forces try to improve co-ordination with their Afghan counterparts in order to eventually transfer more security operations to them.