Samsung must stop importing some models of smartphones and tablet computers into the U.S. after President Barack Obama’s administration upheld a ban won by Apple in a patent-infringement dispute. “After carefully weighing policy considerations, including the impact on consumers and competition, advice from agencies, and information from interested parties, I have decided to allow” the import ban to proceed, Obama’s designee, U.S. Trade Representative Michael Froman, said in a statement on Tuesday. The companies are the largest in the $279.9 billion global smartphone market, with Samsung holding the title of world’s biggest. Patent litigation on four continents, which has cost the companies hundreds of millions of dollars in legal fees, has left no clear winner, with each seeking the biggest prize of limiting the other’s sales in the U.S.