US President Donald Trump said on Wednesday he prevented a war between India and Pakistan this year by threatening both nations with 250% tariffs, the highest he has mentioned on any country.

"If you look at India and Pakistan ... they were going at it,” Trump said at the Asia-Pacific summit in South Korea. "Seven planes were shot down. They were really starting to go.”

Trump said he called Indian Prime Minister Narendra Modi and Pakistan’s leaders to say that Washington would halt trade and impose the massive tariffs if the fighting that briefly flared up in May continued.

“I said I was going to put 250% on each country, which means you’ll never do business ... That’s a nice way of saying we don’t want to do business with you,” Trump said, to applause from the audience, as he referred to trade deals with several Asian countries in a speech.

Trump has previously made similar assertions about warning both countries of a halt in trade during the military strikes - assertions that India has dismissed.

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India's foreign ministry has previously said that Modi confronted Trump during a phone call between the two leaders in June, saying no discussion about US-India trade or US mediation took place during the four-day conflict.

New Delhi says the decision to cease hostilities was taken following a request from Pakistan. Pakistan thanked Trump for playing a mediating role and nominated him for a Nobel Prize for stopping the war.

Trump said both sides initially resisted his call for a ceasefire, but later backed down.

“They both said, ‘No, no, no, you should let us fight.' After literally two days, they called up and said, ‘We understand’, and they stopped fighting,” he said.

Washington has subsequently imposed punitive tariffs of up to 50% on certain Indian goods, including an additional 25% levy from August 27 over New Delhi's continued purchases of Russian oil, even as both sides hold talks on a trade deal.

Trump has lowered Pakistan tariffs to 19% from an initial 29%.