A new US Air Force will build a "mission planning" and operations centre in Darwin, as part of $630 million in American spending across the top end over the next two to three years.

The "Squadron Operations Facility" in Darwin will add to its growing array of military assets in the north, raising fears Australia may be locked into any future military conflict between China and the USA.

The tender documents say the Squadron Operations facility in Darwin will be used for maintenance, mission planning, intelligence and crew briefings — it is budgeted to cost $US26 million ($40 million).

“Being able to organise and deploy forces outside of the dense missile attacks that China is likely to use against places like Guam and Okinawa is part of the strategic logic,”