By Ju-min Park and Jihoon Lee

SEOUL (Reuters) -South Korea's acting President Han Duck-soo on Tuesday spoke with President Donald Trump over the phone, a day before Trump's 25% tariff on the Asian ally is scheduled to kick in.

It is the first time Trump spoke with any of South Korea's acting leaders since he took office in January, while now-impeached President Yoon Suk Yeol, with whom Trump had a phone call the day after his election victory last November, was suspended from duties.

The phone call between Han and Trump also comes as South Korea's trade minister is traveling to the United States to meet with his counterpart for negotiations over tariffs.

Minister Cheong In-kyo, who will meet U.S. Trade Representative Jamieson Greer during the visit, said on Tuesday that the government has been considering measures to increase imports from the United States as he headed to Washington to negotiate over U.S. tariffs.

Cheong also said it was good news ahead of his visit that Trump said the door was open for talks over tariffs with nations other than China.

"It is difficult to reduce exports, so shouldn't we then increase (U.S.) imports? In that regard, we have been reviewing many different packages of measures to resolve the trade balance problem," Cheong said, before flying to Washington.

He noted that the government had had internal discussions about increasing LNG imports from the United States.

Cheong added he will dispute Washington's calculation of its 25% tariff on South Korea, which he called "problematic" given the two countries' existing free trade pact.

Trump also announced a 46% duty for Vietnam, where major South Korean conglomerates like Samsung and LG manufacture products. That will deal a "huge blow" to South Korean exporters with production bases there, Finance Minister Choi Sang-mok said on Tuesday.