The United Kingdom and Australia inked a new defence agreement in Canberra on Thursday, as they try to boost a fledgling nuclear-powered submarine program with the United States.

UK defence minister Grant Shapps signed the agreement in Canberra with his counterpart Richard Marles, establishing a legal framework that makes it easier to host troops and share military intelligence.

The agreement stops short of a full mutual defence pact, which would bind one side to intervene if the other was attacked.

But it does include a "commitment to consult" about emerging threats and establishes an "status of forces agreement", which makes it easier to host soldiers from the other nation.

"It is extraordinary, actually, the United Kingdom and Australia didn't already have a defence cooperation treaty in place," Shapps said after the signing ceremony.

Alongside the United States, Australia and the UK are members of the fledgling AUKUS defence alliance -- a landmark pact aimed at curbing Chinese military expansion in the Asia-Pacific.

Barely two years old, there are already signs the AUKUS program is under threat -- and some fear Donald Trump could scrap it completely if he returns to power next year.

Australian National University security analyst David Andrews said Thursday's agreement gave the stalling AUKUS plan some much-needed momentum.

"If there was a Trump administration at end of year, and for whatever reason they were not interested in pursuing the agreement, or not in the same way it is envisioned now, there is potential for a heavier bilateral pathway," Andrews told AFP.

A major pillar of the AUKUS pact is a promise to help Australia build and acquire a fleet of potent nuclear-powered submarines, one of its biggest-ever military upgrades.

Thursday's agreement would make it easier, for example, for Australian sailors to train on the UK's nuclear subs, or for British crews to be based in Australia.

"This is a reflection of increased engagement between our two defence forces," said Australian defence minister Marles.

"And it will greatly streamline the ability for us to work together."

- Consult on threats -

London and Canberra have pledged to consult each other if looming regional threats start veering towards conflict.

"I think one of the most important elements is it describes a mechanism by which we consult when either of our countries are under threat," said Shapps.

Australia is deeply involved in US-led efforts to counter China's increasingly assertive behaviour in the Asia-Pacific.

Among a host of other initiatives included in the deal is "closer collaboration on undersea warfare", and greater UK contribution to Australian-hosted joint military exercises.

Australia has also agreed to join a coalition with the UK and Latvia that aims to supply drones for the Ukrainian war effort.

The UK has been a major backer of Ukraine in its grinding war against invading Russian forces.

Australia joins drone coalition to help Ukraine war

Australia said Thursday it would join an international drone coalition to aid Ukraine's war effort, uniting with allies like Britain and Latvia.

"It's an important way to make our contribution to the effort to have Ukraine stay the course and be able to resolve this conflict on its own terms," Australian defence minister Richard Marles said.

Ukraine has relied on the massive use of drones to compensate for a shortage of artillery shells as it tries to face down Russia's invasion.

In the two-year war, hundreds of thousands of drones have been deployed for a range of missions, from striking targets hundreds of kilometres away, to reconnaissance, to attacking nearby enemy troops.

Ukrainian President Volodymyr Zelensky has vowed to produce one million drones this year. Ukrainian officials have told AFP the armed forces needed between 100,000 to 120,000 drones per month, making outside help essential.

Australia made the announcement as Canberra hosted UK defence minister Grant Shapps.

Last month Britain and Latvia agreed to lead the drone coalition aimed at delivering thousands more unmanned aerial vehicles to Ukraine.

Shapps said drones had barely featured when the war began, but are "now playing increasingly a significant and sophisticated part".

"Countries that invest in the drone coalition are not just doing it (for) Ukraine -– although that is the primary purpose -- but also because that stands as a potential to bring huge technological improvements and advances to our home markets," Shapps added.

Further details about Australia's commitment are expected to be made public in the coming weeks.

London has said it would allocate £200 million ($250 million) to provide "the single largest package of drones given to Ukraine by any nation".

The most common drones on the battlefield, which Britain is providing to Ukraine in the thousands, are so-called First Person View (FPV) drones.

They allow pilots to see live images of the ground, locate enemy units and, if armed with explosives, attack them from within a few kilometres.

Australia operates several surveillance and other drones, and has put hundreds of millions of dollars into developing the MQ-28A Ghost Bat drone, which can travel thousands of kilometres.