United States Steel Corp. shares surged to their highest level since April 2011 after President Trump announced on Truth Social his full backing of a partnership between the Pittsburgh-based steelmaker and Japan's Nippon Steel.

Trump confirmed that U.S. Steel will remain headquartered in Pittsburgh, calling the deal the largest investment in Pennsylvania's history and a first critical step in revitalizing the nation's steel industry, aligning with his 'America First' agenda of rebuilding critical supply chains. 

"I am proud to announce that, after much consideration and negotiation, US Steel will REMAIN in America, and keep its Headquarters in the Great City of Pittsburgh," Trump wrote on Truth Social. 

He continued, "For many years, the name, "United States Steel" was synonymous with Greatness, and now, it will be again. This will be a planned partnership between United States Steel and Nippon Steel, which will create at least 70,000 jobs, and add $14 Billion Dollars to the U.S. Economy." 

The president said much of the investment will unfold over the next 14 months and will be "the largest Investment in the History of the Commonwealth of Pennsylvania."

Trump concluded the post by stating: "My tariff policies will ensure that steel will once again be, forever, MADE IN AMERICA. From Pennsylvania to Arkansas, and from Minnesota to Indiana, AMERICAN MADE is BACK. I will see you all at U.S. Steel in Pittsburgh on Friday, May 30, for a BIG rally."

Earlier, a Wall Street Journal report said that Nippon sweetened the deal by "roughly doubling its spending plan and even pledging to build a brand-new mill to win Washington's blessing for its takeover of U.S. Steel." 

While Trump initially criticized the deal, he has since warmed to it because it aligns with America First's policy goals of bolstering domestic supply chains and revitalizing manufacturing. 

The merger agreement between U.S. Steel and Nippon, which values U.S. Steel at $55 per share, expires June 18 unless extended.

Shares of U.S. Steel jumped to the highest level since April 2011 following the president's Truth Social post. 

Meanwhile, the United Steelworkers union remains strongly opposed, citing Nippon's history of undercutting U.S. steel markets.