Trump also said if he wins the election, he will call Russian President Vladimir Putin and Zelenskiy and urge them to reach a deal to end the Russia-Ukraine war.
"I think Zelenskiy is the greatest salesman in history. Every time he comes into the country, he walks away with 60 billion dollars," Trump said in a rally in Pennsylvania.
"He wants them to win this election so badly but I would do (it) differently - I will work out peace."
Zelenskiy and Harris' campaign had no immediate reaction to Trump's remarks, and Trump gave no details of his peace plan.
Volodymyr Zelenskiy is hopeful Trump will maintain US military support for Ukraine if he wins. (AP PHOTO)
Zelenskiy arrived in the United States on Sunday to attend sessions at the UN General Assembly and urged his partners to help achieve "a shared victory for a truly just peace."
Washington and its allies have provided a multi-billion dollar assistance program to Ukraine since the Russian invasion began in February 2022, while also imposing several rounds of sanctions against Moscow.
Trump has consistently described US aid to Ukraine as a waste of money and has declined to say he wants Ukraine to win. While Trump and Zelenskiy talked over the phone in July, they have not talked in person since Trump's 2017-2021 term.
Zelenskiy has previously said he cannot predict what Trump would do if he won in November, but hoped the Republican would maintain US military support for Ukraine.
Earlier Trump vowed to slap a 200 per cent tariff on John Deere's imports into the United States if the agricultural equipment company moved production to Mexico as planned.
"As you know, they've announced a few days ago that they are going to move a lot of their manufacturing business to Mexico," he said at an event held in western Pennsylvania.
"I am just notifying John Deere right now that if you do that, we are putting a 200 per cent tariff on everything that you want to sell into the United States."
Earlier this year, John Deere announced that it was laying off hundreds of employees in the American Midwest and increasing its production capacity in Mexico, a decision that upset workers and some political leaders.
John Deere announced plans to increase its production in Mexico. (AP PHOTO)
A representative for the company did not respond to a request for comment about Trump's tariff threats.
Speaking to a gathering of farmers in a rural area outside of Pittsburgh, Trump also said he would press Chinese President Xi Jinping to honour a deal to purchase $US50 billion of US agricultural goods.
During the so-called "Phase 1" trade deal inked between China and the United States during Trump's 2017 to 2021 term, the United States agreed to cut some tariffs on Chinese goods in exchange for pledges to purchase more American agricultural products, energy and manufactured goods. At the time, Trump said China would buy $US50 billion in US agricultural products, though Chinese purchases fell well short of that figure.
"Probably my first call - I'm going to call President Xi - I'm going to say you have to honour the deal you made. We made the deal, you buy $US50 billion worth of American farm products, and I guarantee you, he will buy it, 100 per cent he will buy it," Trump said.
Vice President Kamala Harris is due to campaign in the state of Pennsylvania later this week. (AP PHOTO)
Harris is also visiting Pennsylvania on Wednesday.
Trump leads among likely voters in the battleground states of Arizona, Georgia and North Carolina, outpacing Harris six weeks before the November 5 presidential election, a New York Times/Siena College poll suggested.
Trump bested his Democratic rival 50 per cent to 45 per cent in Arizona last week, 49 per cent to 45 per cent in Georgia and 49 per cent to 47 per cent in North Carolina, according to the poll, which echoed other recent polls showing a close contest.
with AP
