Washington DC - President Donald Trump on Thursday said he was considering imposing a 15% or 20% blanket tariff on countries that had not yet received specific notifications, effective August 1.

Trump this week began issuing letters to many US trading partners as he ramps up pressure for more favorable trade deals.

In his letters to leaders from more than 20 countries, Trump outlined duties ranging from 20% to 50% – in the case of Brazil – that would take effect on August 1.

Trump's letters warn that if the recipients raise their tariffs, the US would retaliate with even higher rate increases.

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When asked by NBC News what would happen to countries that did not receive letters, he floated the idea of the 15% or 20% rates.

"We're just going to say all of the remaining countries are going to pay, whether it's 20% or 15%. We'll work that out now," Trump was quoted as saying by NBC News.

It was not clear whether this meant an increase from Trump's 10% baseline tariffs on goods currently paid by most countries, or if it would apply only to those subject to higher rates than the baseline.

The tariffs are part of Trump's "Liberation Day" trade announcement in April, a sweeping package of import duties that were to take effect on July 9, but are now pushed off to August 1 as trade talks continue.

The policy imposed the universal 10% tariff on nearly all imports, with much higher, country-specific "reciprocal" tariffs for dozens of countries.