WASHINGTON (Reuters) -U.S. President Donald Trump on Friday accused China of violating a bilateral deal to roll back tariffs and announced a doubling of worldwide steel tariffs to 50%, once again rattling international trade.

Trump said China had violated an agreement with the U.S. to mutually roll back tariffs and trade restrictions for critical minerals and issued a new veiled threat to get tougher with Beijing.

"China, perhaps not surprisingly to some, HAS TOTALLY VIOLATED ITS AGREEMENT WITH US. So much for being Mr. NICE GUY!," Trump said in a post on his Truth Social platform.

Later, at a rally in Pennsylvania promoting an impending "partnership" between Japan's Nippon Steel and U.S. Steel, he announced the U.S. would double steel tariffs from 25% to 50%, effective next week, which he said "will even further secure the steel industry in the United States."

While China is the world's largest steel producer and exporter, very little is sent to the United States, as a 25% tariff imposed in 2018 shut most Chinese steel out of the market.

On overall trade with China, Trump said he made a "fast deal" in mid-May with Chinese officials for both countries to back away from triple-digit tariffs for 90 days. He said he did this to save China from a "devastating" situation, factory closings and civil unrest caused by his tariffs of up to 145% on Chinese imports.

Trump did not specify how China had violated the agreement made in Geneva, Switzerland, or what action he would take against Beijing.

Asked later on Friday in the Oval Office about the China deal, Trump said: "I'm sure that I'll speak to President Xi, and hopefully we'll work that out."

RARE EARTHS LICENSES

But a U.S. official told Reuters that it appeared China was moving slowly on promises to issue export licenses for rare earths minerals. The deal called for China to lift trade countermeasures that restrict its exports of the critical metals needed for U.S. semiconductor, electronics and defense production.

"The Chinese are slow-rolling their compliance, which is completely unacceptable and it has to be addressed," U.S. Trade Representative Jamieson Greer told CNBC, without specifying how that would happen.

Indeed, Reuters reported on Friday that global auto executives are sounding the alarm on an impending shortage of rare-earths magnets from China - used in everything from windshield-wiper motors to anti-lock braking sensors - that could force the closure of car factories within weeks. 

Liu Pengyu, a spokesperson for China's embassy in Washington, said China has maintained communications on trade matters with U.S. counterparts since the Geneva talks, but raised concerns about U.S. export controls.

"China once again urges the U.S. to immediately correct its erroneous actions, cease discriminatory restrictions against China and jointly uphold the consensus reached at the high-level talks in Geneva," Liu said in a statement.

Reuters reported earlier this week that the U.S. has ordered a broad swath of companies to stop shipping goods to China without a license and revoked some existing export licenses, according to three people familiar with the matter. 

Products affected include design software and chemicals for semiconductors, butane and ethane, machine tools and aviation equipment, these sources said.

Spokespersons for the White House, the U.S. Treasury and the U.S. Trade Representative's Office did not respond to requests for comment.

CHINA TALKS 'STALLED'

On Thursday, Treasury Secretary Scott Bessent told Fox News Channel that U.S. trade talks with China were "a bit stalled" and that getting a deal over the finish line will likely need the direct involvement of Trump and Xi. 

The U.S.-China agreement two weeks ago to dial back triple-digit tariffs for 90 days prompted a massive relief rally in global stocks, and along with other pauses on Trump's import taxes, lowered the effective U.S. tariff rate to the mid-teens from around 25% in early April. It was less than 3% when Trump took office in January.

The temporary truce between Washington and Beijing, however, had done nothing to address the underlying reasons for Trump's tariffs on Chinese goods, mainly longstanding U.S. complaints about China's state-dominated, export-driven economic model, leaving those issues for future talks.

Major U.S. stock indexes ended little changed on Friday after Trump's complaint about China's compliance. Trump's social media post came two days after a reporter infuriated him by asking him about Wall Street's new term for bets that he will back off extreme tariff actions - the "TACO" trade, an acronym coined by a Financial Times columnist for "Trump Always Chickens Out."

"I chicken out? Oh, I've never heard that. You mean because I reduced China from 145% that I set, down to 100 and then to another number?" Trump said, later adding: "It's called negotiation."

Trump's tariff strategy also suffered a major setback on Wednesday when the U.S. Court of International Trade ruled that his broad global tariffs, including those on China, were invalid because he exceeded his authority under an emergency powers law used to back them. An appeals court has issued a temporary stay for the decision, allowing them to remain in place for now.