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.

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.

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

Ukraine's war against invading Russian forces "matters to all of us," he said, opening the 25th meeting of the Ukraine Defense Contact Group.

"We all have a stake in ensuring that autocrats cannot place their imperial ambitions ahead of the bedrock rights of free and sovereign peoples."

- 'World is watching' -

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.

The European Union's foreign policy chief Kaja Kallas said she hoped the United States would keep supporting Ukraine.

If not, she added, the EU was ready to take the lead.

"I'm really sure that all the other members, and hopefully also the United States, are ready to continue with the support to Ukraine," Kallas said as she headed to the Ramstein meeting.

At this stage, she told journalists, "we shouldn't really speculate" about future US support. But she did say that it "is not in the interest of America that Russia will be the strongest force in the world".

She added that "the European Union is also ready to take over this leadership if the United States is not willing to do so".

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.

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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