A US Marine who arrived in the NT on July 8 has tested positive to Covid-19.

The woman, aged 22, was undertaking a mandatory 14 day quarantine at Bladin Village when she tested positive in the past 24 hours.

She has mild symptoms and is under the care of NT Health at the NT Centre for National Resilience.

The total number of cases diagnosed in the Northern Territory is 190.

Documents about the controversial decision to allow foreign military personnel to quarantine in a Darwin CBD hotel will remain secret, with a Freedom of Information request rejected on the grounds they could be “susceptible to mischievous interpretation” and “lead to mistrust”.

dozens of pages of correspondence between senior officials — were "brought into existence" for a Cabinet sub-committee, making them exempt under the Information Act.

The department also said releasing the information would provide a "one-sided" view and that disclosure of alternative ideas floated in the correspondence would "likely lead to ill-informed debate" about the department's final decision.

With more than 2000 Marines in Australia's north, commander USMC Colonel David Banning says the force isn't just in the Top End to train, it's ready for action.

USMC Colonel David Banning insists his troops are ready for action.

The declaration comes as Defence Minister Peter Dutton hints that while maintaining peace is a "first priority", the visiting Darwin-based force could soon swell amid growing Indo-Pacific tension.

"As military members, it's our job to be prepared for the greatest range of what-if possible"

Defence Minister Peter Dutton wants to bolster US marine numbers in the Top End beyond 2500, declaring the nation’s security depends on even closer military ties with our closest ally.

Mr Dutton told the Australian Strategic Policy Institute’s annual conference in Canberra yesterday Australia was working to take greater responsibility for its own security, but needed to “become an even more reliable alliance partner” to the US.

He said there was scope to increase the size of the US marine rotational force in the Top End from its 2500-strong pre-Covid high.

Chief Minster Michael Gunner has indicated he’s open to working with the Commonwealth and US governments on the issue.

“I think most Territorians know about the Bombing of Darwin and that young Americans died here that day too, defending this place that we call home."

Australia could soon be hosting more US marines and warships with Defence Minister Peter Dutton declaring he wants even greater military cooperation with our closest ally.

Senior officials from both nations are discussing options for expanded military cooperation, which the ABC has learnt include a proposal to form a new joint US marines and ADF training brigade based in Darwin.

If established, the joint brigade would be the first of its kind for Australia and would likely involve a rotating command with the United States.

Mr Dutton agreed there was scope to increase the size of the US marine rotational force in the Top End from its pre-COVID level of 2,500, and to base US navy vessels at HMAS Stirling near Perth. acting US ambassador Michael Goldman declined to comment on whether more American marines could soon be heading to Australia.