US President Donald Trump has warned Russia that it will face "very severe consequences" if Russian President Vladimir Putin will not agree to stop the war in Ukraine after their upcoming Alaska summit.

Trump issued the threat on Wednesday during an event at the Kennedy Center in Washington, which took place after he joined a video conference with European leaders and Ukrainian President Volodymyr Zelenskyy.

They discussed the path to peace and territorial issues during the call, which had been arranged by German Chancellor Friedrich Merz.

The Trump-Putin meeting will take place on Friday in Anchorage.

When Trump was asked if Russia would face tariffs or sanctions, he said, "There will be consequences." But would not say what they would be.

He also said that if the summit went okay, "We'll have a quick second meeting between President Putin and President Zelenskyy and myself, if they'd like to have me there."

Zelenskyy doubled down on his stance that his country must be involved in any ceasefire negotiations, and said he wanted to prepare for trilateral talks.

He said: "I would like to emphasize right away that any issues related to the territorial integrity of our state cannot be discussed without regard to our state, our people. The will of the state, the will of our people and the Constitution of Ukraine."

French President Emmanuel Macron echoed this view when he provided an update on the call. He said Trump agreed that "territorial issues that fall within Ukraine's jurisdiction can be negotiated and will only be negotiated by the Ukrainian president."