The Australian Defence Force on Thursday confirmed the nationality of the soldiers who were serving in southern Uruzgan province, where around 1,500 Australian troops are based. It said families in Australia were being informed of the deaths.

The deaths bring to 15 the number of foreign soldiers killed this month in insider attacks. NATO-led forces have increased security to try to prevent them, including requiring soldiers to carry loaded weapons at all times on bases.

US Joint Chiefs of Staff chairman Martin Dempsey visited Kabul last week to discuss the worrying increase in rogue shootings. US President Barack Obama also expressed his "deep concern" over the insider attacks.

Dempsey urged Afghan officials to take tougher preventative action, although Western commanders have ruled out cutting back training and support between NATO-led troops and their Afghan allies.

The killings, many of which have been claimed by the Taliban as evidence of their ability to infiltrate Afghan security forces, are particularly worrying as security transition plans gather pace.

Under those plans, all foreign combat troops are due to leave Afghanistan by the end of 2014. The alarming rise in rogue shootings has raised more questions about the readiness of Afghan forces to take over.

Including Wednesday's shooting, there have been 34 insider attacks this year, leading to 45 coalition deaths, the majority of them Americans.