Republican presidential candidate Donald Trump said Friday he had spoken by telephone with Ukraine leader Volodymyr Zelensky, and pledged to end the European country's war with Russia.

"I appreciate President Zelensky for reaching out because I, as your next President of the United States, will bring peace to the world and end the war that has cost so many lives and devastated countless innocent families," Trump said in a post on his Truth Social platform.

"Both sides will be able to come together and negotiate a deal that ends the violence and paves a path forward to prosperity."

The US has provided tens of billions of dollars in military assistance for Kyiv since Russia launched its full-scale invasion of Ukraine in February 2022 – though a Trump victory in the November election would put Washington's continued support into question.

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Zelensky confirmed the call, during which he congratulated Trump on formally becoming the Republican Party's presidential nominee, as well as wishing the 78-year-old well after an attempt on his life a week ago.

"We agreed with President Trump to discuss at a personal meeting what steps can make peace fair and truly lasting," Zelensky said in a post on X.

"I noted the vital bipartisan and bicameral American support for protecting our nation's freedom and independence," he said.

Trump has repeatedly claimed he would end the war very quickly, without offering details as to how.

Last week, the ex-president hosted at his Florida estate Hungary's Prime Minister Viktor Orban, who met with Russian President Vladimir Putin earlier this month.

Trump's frequent praise for Putin and reluctance to outright criticize the Russian invasion have stirred concerns among Ukraine's allies that he would force the country into accepting partial defeat.

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He has also repeatedly suggested backing away from NATO, even saying he would encourage Russia to attack any members who had not met their financial obligations.

Trump's running mate J.D. Vance has also argued the US should drop aid to Ukraine. The senator opposed the approval of $61 billion in new military aid for Ukraine, which was stalled for months earlier this year.

Trump told the Republican National Convention in Milwaukee on Thursday that he would bring an end to raging international crises, saying he could "stop wars with a telephone call."

"I will end every single international crisis that the current administration has created, including the horrible war with Russia and Ukraine," Trump said, without elaborating on how.

Zelensky said earlier this week that he and Trump would "work together" if the Republican won the White House.

"I'm not worried about this," he told a news conference.

Zelensky declined to say whether he was worried about President Joe Biden, who has been facing calls to drop his reelection campaign following a disastrous debate performance and questions over his health and mental acuity.

He did, however, acknowledge that "turbulence" during the US election cycle was having a "big impact" on his country.

Trump's relationship with Zelensky famously goes back to his time in the White House.

In 2019, Trump was impeached for withholding military aid to Ukraine while pressuring Zelensky to help him dig up dirt on his election rival Biden – a race he went on to lose in 2020.