US Defence Secretary Lloyd Austin is expected to announce a substantial new military aid package for Kyiv at the 25th such talks at Ramstein Air Base that will include representatives from some 50 countries.

Ukrainian president Zelensky only confirmed late Wednesday that he will fly in for the meeting.

NATO Secretary General Mark Rutte and EU foreign policy chief Kaja Kallas were also expected at the Ukraine Defence Contact Group meeting starting at 1000 GMT alongside German Defence Minister Boris Pistorius.

Russian and Ukrainian forces now engaged in fierce fighting in the almost three-year-old war are looking to secure their battlefield positions before Trump's January 20 inauguration.

Once back in office, Trump, who has criticised 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 United States under President Joe Biden has been Ukraine's biggest wartime backer, providing military aid worth more than $65 billion since February 2022, and a senior US defence official told journalists this week that a "substantial announcement" on aid is likely to come at the Thursday meeting.

Germany has been Ukraine's second-biggest backer at some $30 billion so far, including money committed for this year.

Austin told AFP on Wednesday that US leadership on Ukraine is "critical," and said continued military assistance for Kyiv is key.

- 'It's not over' -

"We've not just asked countries to provide security assistance -- we have led the way in every case in terms of the amount of security assistance that we've provided, the speed at which we got that security assistance there," he said at Ramstein.

"It's real important for the entire coalition to continue to provide military aid. Now, the US has led this effort, and hopefully... will continue to do so, because it's not over," Austin said.

The US defence chief launched the process that has coordinated the delivery of jets, tanks, missiles, air defences and other weapons to Ukraine, but uncertainty looms as Trump prepares to take office again.

Trump has questioned backing for Ukraine and criticised NATO allies for spending too little on shared defence.

He also threatened during his previous term to withdraw many of the 35,000 US troops stationed in Germany.

Trump sparked further alarm among allies this week by refusing to rule out military action to take Greenland, an autonomous territory of EU and NATO member Denmark, and calling the US-Canada border an "artificially drawn line".

Since the start of Russia's offensive in February 2022 when it failed to seize the Ukrainian capital Kyiv, Moscow has adapted its aims, concentrating instead on trying to conquer eastern Ukraine.

Russia said Monday its forces had captured the "important logistics hub" of Kurakhove in eastern Ukraine after months of steady gains in the area.

The claim came after Russia said Kyiv had launched a new "counterattack" in its Kursk border region, five months after Ukraine's forces initially seized swathes of the area in a shock cross-border incursion.

Zelensky has voiced hope and said Trump would be crucial to any end of the conflict, in an interview with US podcaster Lex Fridman released Sunday.

"Trump and I will come to an agreement and... offer strong security guarantees, together with Europe, and then we can talk to the Russians," Zelensky said, according to the published translation.

He added that Trump "has enough power to pressure him, to pressure Putin".