The Turnbull government has formally declined a request from the US to increase its military commitment in the Middle East campaign against Islamic State.

US Defence Secretary Ash Carter in December asked coalition partners fighting the extremist group in Iraq and Syria to consider expanding their contribution in the wake of terror attacks in Paris.

Defence Minister Marise Payne confirmed on Wednesday that Australia had rejected the request and would maintain its current contribution.

"Australia has considered the request from US Secretary of Defense Ash Carter in light of the substantial contributions we are already making to train Iraqi security forces and to the air campaign," a spokesman for the Minister said.