The secretary of state was speaking at the start of a day of Brussels talks with NATO and EU officials to urgently address ramping up support for Kyiv before Donald Trump reclaims the White House -- potentially jeopardising future aid.

Addressing reporters alongside NATO chief Mark Rutte, Blinken said they had discussed the fact North Korean forces have been "injected into the battle, and now, quite literally, in combat which demands and will get a firm response."

The US State Department confirmed Tuesday that Pyongyang's troops -- whose entry into the conflict marks a potentially major escalation -- have begun "engaging in combat operations" alongside Russian forces near the border with Ukraine.

A spokesman said that of the more than 10,000 North Korean soldiers sent to eastern Russia, "most of them have moved to the far western Kursk Oblast, where they have begun engaging in combat operations with Russian forces".

Rutte meanwhile stressed the crucial role played by China in helping Russia's "war effort", as well as Iranian weapons deliveries -- paid for with Russian funds that were in turn helping Tehran to "destabilize the Middle East".

Blinken was taking part in a meeting of the North Atlantic Council, NATO's decision-making body, before talks with European Union top diplomat Josep Borrell, his successor Kaja Kallas and Ukraine's Foreign Minister Andriy Sybiga.

His emergency trip comes as Trump's election victory, coupled with a political crisis in Germany, heightens fears about the future of assistance for Ukraine at a key point in the fight against Russia's invasion.

Trump has in the past voiced admiration for Russian President Vladimir Putin and scoffed at the $175 billion the United States committed for Ukraine since the start of the war in 2022.

The 78-year-old tycoon, who will be inaugurated on January 20, spoke with Ukrainian President Volodymyr Zelensky after winning re-election following a first stint as president between 2017 and 2021.

He has boasted he can end the war in a day, likely by forcing concessions from Ukraine, although his newly named national security advisor, Mike Waltz, said Trump may also pressure Putin.

The Washington Post reported the Republican leader also held a phone call with Putin and discouraged an escalation by Russia. The Kremlin denied the report.

US media reported Trump might pick Republican Senator Marco Rubio to replace Blinken as secretary of state.

Rubio is seen as supportive of Kyiv but has also said Washington should show "pragmatism" rather than sending billions of dollars more in weapons as the war hit a "stalemate".

- 'As long as it takes' -

The Biden administration has made clear it plans in its remaining weeks to push through the more than $9 billion of remaining funding appropriated by Congress for weapons and other security assistance to Ukraine.

Mark Cancian, senior advisor at the Center for Strategic and International Studies, expected the United States to focus in particular on sending vehicles, medical supplies and small-arms ammunition, which Ukraine needs and the United States can provide.

"Between now and the end of the administration, they're going to try to ship everything they can that's available," Cancian said.

Despite Kyiv's pleas it seems unlikely, however, that Washington will lift its veto on Ukraine's use of long-range missiles to strike deep into Russian territory.

Trump in his first term aggressively pushed Europe to step up defence spending and questioned the fairness of the NATO transatlantic alliance -- robustly defended by Biden.

"Whatever approach the US leadership takes towards Ukraine, Europe will have to step up, and we will have to take the lead in supporting Ukraine's defence efforts and macro financial stability," said Olena Prokopenko of the German Marshall Fund of the United States.

"Unfortunately, Donald Trump's win comes at arguably the worst possible time in terms of Europe's political and economic shape and its ability to promptly coordinate".

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