The move is the White House's latest effort to restore President Donald Trump's vision of a near-global tariff after the US Supreme Court in February struck down his "reciprocal" duties of 10 per cent to 50 per cent imposed under a national emergencies law to try to shrink the US trade deficit.
New tariffs had been expected, but trade partners around the world joined in strongly disputing the justification for them.
Some, however, noted they would make little difference to current levies.
The new tariffs cover 99.4 per cent of US imports, but include numerous product exemptions, such as oil and gas, fertiliser and certain food items.
"The United States has had a forced labour import ban for nearly a century, and rigorously enforces it. It's well past time for our trading partners to do the same," US Trade Representative Jamieson Greer said in a statement.
Imposed under Section 301 of the Trade Act, the new duties allow the administration to maintain a tariff floor on virtually all US imports despite the Supreme Court setback.
The tariffs are also likely to face less legal risk as Section 301 has survived court challenges.
Trump's temporary 10 per cent global tariff expired after midnight on Friday, Washington time, after 150 days.
The new duties took effect at that same moment, with goods in transit exempted until July 28.
The US imposed a 10 per cent duty on goods of Argentina, Bangladesh, Britain, Cambodia, Canada, Ecuador, El Salvador, Guatemala, Honduras, India, Indonesia, Jordan, Malaysia, Mexico, Pakistan, Sri Lanka, Trinidad and Tobago.
The European Union, Taiwan, Japan, South Korea and Switzerland were assigned rates that, combined with pre-existing most-favoured-nation tariff rates, totalled 10 per cent or 12.5 per cent.
The other 38 countries, including Australia and China, were assigned a 12.5 per cent rate.
Greer previously pledged that for countries with trade deals with Washington capping US tariff rates, the new forced labour duties would not push them above those caps - a point the EU noted in its response.
"The EU notes positively the fact that this outcome is in line with the US tariff commitments agreed under the EU-US Joint Statement," a European Commission spokesperson said, adding it provided "positive momentum" for exploring further tariff exemptions and deepening co-operation.
Britain said the move would have no negative effects, with a spokesperson noting "our agreement with the US remains in place, and today we see an improvement to our trading terms with zero tariffs on whisky and medical technology".
Trump administration officials have told Chinese counterparts they intend to rebuild Trump's second-term tariffs on Chinese goods back up to the 20 per cent that was agreed upon in a trade truce with Chinese President Xi Jinping in November 2025 - but not exceed that level.
Before Friday's action, China's tariff rate had fallen to 10 per cent, excluding the 25 per cent imposed during Trump's first term on industrial goods.
The action drew stronger protests from some trade partners.
Australia and Brazil described the new tariffs as unjustified and said they would seek to have them removed, while Norway said there was "no basis" for them.
Canada - hit on Monday with new Trump tariffs on $US20 billion ($A29 billion) worth of goods - issued a muted response, with minister for US trade Dominic LeBlanc saying Canada "will continue engaging constructively with the United States on this matter".
Many goods will be exempted from the duties, including oil and gas, fertiliser, certain foodstuffs and goods already subject to national security tariffs, such as autos, steel, aluminium and copper.
Aircraft and parts will also be exempted, along with critical minerals.
