Zelensky spoke at a meeting of about 50 allies at the US air base Ramstein in Germany, the last such gathering before Trump takes office on January 20, casting doubt on future American support for Kyiv.

"It's clear that a new chapter starts for Europe and the entire world -- just 11 days from now, a time when we have to cooperate even more, rely on one another even more, and achieve even greater results together," said Zelensky.

"I see this as a time of opportunities," he added at the 25th meeting of the Ukraine Defence Contact Group.

As the grinding war nears the three-year mark, Zelensky repeated a call for Western allies to send troops to help Ukraine.

"Our goal is to find as many instruments as possible to force Russia into peace," he told the meeting. "I believe that such deployment of partners' contingents is one of the best instruments."

The United States under President Joe Biden has been Ukraine's biggest wartime backer, providing military aid worth more than $65 billion since February 2022.

- 'Success story' -

US Defense Secretary Lloyd Austin -- who launched the Ramstein format shortly after the war started -- announced new military aid worth $500 million for Kyiv.

"The coalition to support Ukraine must not flinch. It must not falter. And it must not fail," Austin said. "Ukraine's survival is on the line. But so is all of our security."

Austin looked back over recent years and how, since the days when "Ukrainian citizens were making Molotov cocktails to defend their homes," the multinational group had supplied the country with an arsenal of high-tech weapons.

This had helped "turn Ukraine's struggle into one of the great military success stories of our times," Austin said, adding that Russia had suffered more than 700,000 dead or wounded and had become "more isolated" on the world stage.

Austin said "this coalition must continue to stand foursquare with Ukraine -- and to strengthen its hand for the negotiations that will someday bring Putin's monstrous war to a close".

But, pressed on whether he wanted the Trump administration to push on with the effort, Austin said that "it's up to the future administration to make their own decisions".

Trump, who has criticised the large amount of US military aid for Kyiv, has promised to bring a swift end to the war, but without making any concrete proposals for a ceasefire or peace deal.

EU foreign policy chief Kaja Kallas said she hoped the United States would keep supporting Ukraine but added that "the European Union is also ready to take over this leadership if the United States is not willing to do so".

German Defence Minister Boris Pistorius called for the continuation of the Ramstein format, saying its results so far "must now inspire us to make every effort for what is still to come".

- 'World is watching' -

Russian and Ukrainian forces are now engaged in fierce fighting, looking to secure their battlefield positions before Trump's inauguration.

Trump has criticised NATO allies for spending too little on shared defence. This week, he sparked further alarm by refusing to rule out military action to take Greenland, an autonomous territory of EU and NATO member Denmark.

Austin stressed that "the United States of America has always been a reliable partner. We will always be a reliable partner in the future".

NATO Secretary General Mark Rutte said allies needed to help Ukraine reach a position of strength ahead of any eventual ceasefire or peace talks.

"We have to bring Ukraine into the best possible position that one day, when talks would start at the initiative of Ukraine on how to solve this conflict, that they are in the best possible position to do that," he said.

"And then when these talks end, it will be looked at, in a sense, whether it is a good deal or not.

"And if it is not a good deal, it will be watched by the Chinese, the North Koreans, Iran, obviously, Russia. The whole world is watching."

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