* Trump threatens tariffs to curb Iran's purchases of

weapons

* US Supreme Court has curtailed Trump's tariff

authorities

* Reuters has reported Iran sought Chinese missiles,

chipmaking tools

By David Lawder and Susan Heavey

WASHINGTON, April 8 (Reuters) - U.S. President Donald

Trump said on Wednesday that imports from countries supplying

Iran with military weapons will face immediate 50% tariffs with

no exemptions, threatening the new duties just hours after

agreeing to a two-week ceasefire with Tehran.

After more than five weeks of air strikes against Iran's

missile launchers, military installations and weapons industry,

Trump returned to a favorite foreign policy pressure tool -

tariffs - effectively warning China and Russia in a social media

post against restocking Tehran's military inventories.

But the U.S. Supreme Court stripped the U.S. president of

his fastest and broadest tariff authority, the International

Emergency Economic Powers Act, in February when it ruled that

his broadest global tariffs imposed under the 1977 law were

illegal.

"A Country supplying Military Weapons to Iran will be

immediately tariffed, on any and all goods sold to the United

States of America, 50%, effective immediately, There will be no

exclusions or exemptions! President DJT," Trump wrote on the

Truth Social site, without naming any countries.

China and Russia have helped Iran build military capacity

to counter U.S. and Israeli pressure, supplying missiles,

air-defense systems and dual-use technologies intended to

bolster deterrence.

That support appeared capped during the U.S.-Israeli attacks on

Iran. Both Beijing and Moscow have denied supplying any weapons

recently, although allegations against Russia have persisted.

Reuters reported in February, prior to the first U.S. and

Israeli strikes on Iran, that Tehran was considering a purchase

of supersonic anti-ship cruise missiles from China. Reuters also

reported in March that China's top semiconductor maker, SMIC

, has sent chipmaking tools to Iran's military,

according to two senior Trump administration officials.

"This is a China-related threat, the way I read it. And China

will read it that way," said Josh Lipsky, vice president and

chair of international economics at the Atlantic Council.

Although drone and missile parts routinely flow from

Chinese entities to Iran, evading U.S. sanctions, Lipsky said

Trump was unlikely to follow through with new tariffs in the

near term because that would derail his planned trip to Beijing

to meet with Chinese President Xi Jinping.

On Tuesday, U.S. Trade Representative Jamieson Greer said

Trump would seek to maintain the current stability in the

U.S.-China relationship, to preserve U.S. access to

Chinese-produced rare-earth minerals and magnets while

maintaining prior tariff levels. Greer said Trump wanted to

avoid a "massive confrontation" with Xi.

ALTERNATIVE TARIFF TOOLS

Of Trump's still available trade tools, an active "Section

301" unfair trade practices action against Chinese goods from

his first term would be the most likely vehicle for adding new

tariffs quickly, Lipsky said.

A more limited tool would be Section 232 of the Cold

War-era Trade Expansion Act of 1962, aimed at protecting

strategic domestic industries on national security grounds, but

it would limit duties to specific sectors, lacking the broad

economy-wide impact of the prior IEEPA-based tariffs.

Trump's tariffs on Chinese goods over nearly eight years

already have cut U.S. imports from China sharply, from a peak of

$538.5 billion in 2018 to $308.4 billion in 2025, with further

declines recorded in January and February of 2026.

Russia has been another source of arms technology for Iran, but

U.S. imports of Russian goods also have shriveled since the

invasion of Ukraine in 2022 and the wave of financial sanctions

imposed on Moscow as a result of that move.

U.S. imports from Russia, one of the only countries not subject

to Trump's now-cancelled "reciprocal" tariffs, jumped 26.1% to

$3.8 billion in 2025. These imports are dominated by palladium,

which is used in automotive catalytic converters, fertilizers

and their ingredients, and enriched uranium for nuclear

reactors. The Commerce Department already is moving to impose

punitive tariffs on Russian palladium after an anti-dumping

investigation.