By Andrea Shalal and Kanishka Singh

ABOARD AIR FORCE ONE (Reuters) -U.S. President Donald Trump said on Wednesday he will announce fresh tariffs over the next month or sooner, adding lumber and forest products to previously announced plans to impose duties on imported cars, semiconductors and pharmaceuticals.

"I'm going to be announcing tariffs on cars and semiconductors and chips and pharmaceuticals, drugs and pharmaceuticals and lumber, probably, and some other things over the next month or sooner," Trump said at a conference in Miami.

Speaking to reporters on Air Force One as he traveled back to Washington, Trump said he was thinking about a 25% tariff on lumber and forest products, to take effect around April 2, when a tariff on autos of around the same amount is expected.

He said he expected tariffs to generate large revenues for the United States, but also offered countries a reprieve if they lowered or removed their own tariffs on U.S. goods.

Trump on Tuesday said he also intends to impose similar duties on semiconductors and pharmaceuticals, the latest in a series of measures threatening to upend international trade.

Those tariffs would also start at "25% or higher", rising substantially over the course of a year. He did not provide a date for announcing those duties and said he wanted to provide some time for drug and chip makers to set up U.S. factories so they can avoid tariffs.

Since returning to office four weeks ago, Trump has imposed an additional 10% tariff on all imports from China over China's failure to halt fentanyl trafficking. He also announced, and then delayed for a month, 25% tariffs on goods from Mexico and non-energy imports from Canada.

Last week, he unveiled plans to slap reciprocal tariffs on all countries that have tariffs on U.S. goods or set up non-tariff barriers to limit U.S. access to their markets.

EU trade chief Maros Sefcovic met with U.S. counterparts - Commerce Secretary Howard Lutnick, Trump's nominee to be U.S. Trade Representative Jamieson Greer and National Economic Council director Kevin Hassett - in Washington on Wednesday to discuss the various tariffs facing U.S. trading partners.

Trump's threats have changed over time, leaving other nations and businesses unclear of what is to come next. Some economists and experts have warned Trump's sweeping tariffs will stoke inflation.

(Reporting by Andrea Shalal and Kanishka Singh; Editing by Leslie Adler and Lincoln Feast.)