Australia has agreed to deploy an additional 30 troops to a training mission in Afghanistan.

Last month NATO requested more Australian training and mentoring forces to help bolster the Afghan army, and US officials then formally approached the Australian Defence Force (ADF).

Defence Minister Marise Payne told a senate estimates hearing the ADF's overall commitment would now rise to 300.

"These additional ADF members will allow Australia to commit additional advisors to further develop the long term capabilities of the Afghan security forces as part of our current train, advise and assist mission," she said.

"Given the centrality of Afghanistan and the global fight against terrorism, enhanced contribution to the support mission is both timely and appropriate.

"These adjustments have been considered by the Government in light of broader ADF commitments across the globe and in view of the extremely dynamic strategic environment in which we currently find ourselves, not least in our own region."

Ms Payne also expressed her "deepest sympathies" to the families, colleagues and friends of the two soldiers — Stuart Redon and private Jason Challis — who recently lost their lives during training exercises.