West Mifflin (United States) (AFP) – US President Donald Trump said Friday that he would double steel and aluminum import tariffs to 50 percent from next week, the latest salvo in his trade wars aimed at protecting domestic industries.

"We're going to bring it from 25 percent to 50 percent, the tariffs on steel into the United States of America," he said while addressing workers at a US Steel plant in Pennsylvania.

"Nobody's going to get around that," he added in the speech before blue-collar workers in the battleground state that helped deliver his election victory last year.

Shortly after, Trump wrote in a Truth Social post that the elevated rate would also apply to aluminum, with the new tariffs "effective Wednesday, June 4th."

Since returning to the presidency in January, Trump has imposed sweeping tariffs on allies and adversaries alike in moves that have rocked the world trade order and roiled financial markets.

The tariffs had seen a brief legal setback earlier this week when a court ruled Trump had overstepped his authority, but an appellate court on Thursday said the tariffs could continue while the litigation moves forward.

Trump has also issued sector-specific levies that affect goods such as automobiles.

On Friday, he defended his trade policies, arguing that tariffs helped protect US industry.

He added that the steel facility he was speaking in would not exist if he had not also imposed duties on metals imports during his first administration.

On Friday, Trump touted a planned partnership between US Steel and Japan's Nippon Steel, but offered few new details on a deal that earlier faced bipartisan opposition.

He stressed that despite a recently announced planned partnership between the American steelmaker and Nippon Steel, "US Steel will continue to be controlled by the USA."

He added that there would be no layoffs or outsourcing of jobs by the company.

Upon returning to Washington late Friday, Trump told reporters he had yet to approve the deal.

"I have to approve the final deal with Nippon, and we haven't seen that final deal yet, but they've made a very big commitment," Trump said.

Last week, Trump said that US Steel would remain in America with its headquarters to stay in Pittsburgh, adding that the arrangement with Nippon would create at least 70,000 jobs and add $14 billion to the US economy.

Trump in Pennsylvania said that as part of its commitment, Nippon would invest $2.2 billion to boost steel production in the Mon Valley Works-Irvin plant where he was speaking.

Another $7 billion would go towards modernizing steel mills, expanding ore mining and building facilities in places including Indiana and Minnesota.

A proposed $14.9 billion sale of US Steel to Nippon Steel had previously drawn political opposition from both sides of the aisle. Former president Joe Biden blocked the deal on national security grounds shortly before leaving office.

There remain lingering concerns over the new partnership.

The United Steelworkers union (USW) which represents thousands of hourly workers at US Steel facilities said after Trump's speech that it had not participated in discussions involving Nippon Steel and the Trump administration, "nor were we consulted."

"We cannot speculate about the meaning of the 'planned partnership,'" said USW International President David McCall in a statement.

"Whatever the deal structure, our primary concern remains with the impact that this merger of US Steel into a foreign competitor will have on national security, our members and the communities where we live and work," McCall said.

"The devil is always in the details," he added.

Trump had opposed Nippon Steel's takeover plan while on the election campaign trail. But since returning to the presidency, he signaled that he would be open to some form of investment after all.