Australia and the United States have agreed to share the cost of the U.S. military's presence in Australia's tropical north, a critical part of President Barack Obama's "pivot" to Asia, Australian Defense Minister Marise Payne said on Thursday.

Payne met U.S. Defense Secretary Ash Carter in Washington this week to discuss plans to double the number of U.S. Marines in the northern city of Darwin from the current 1,250 by 2020, a goal that was delayed earlier this year from 2017 as originally planned.

Australia and the United States signed a "force posture agreement" in 2014 to provide for joint exercises and for U.S. naval and air force deployments. Operational costs until now had been split on an ad-hoc basis, with infrastructure spending withheld.