The department last month banned shipments of American technology to ZTE for seven years, saying the company had failed to reprimand employees who violated American trade controls on Iran and North Korea.

The company had already agreed last year to a $1.2 billion fine in connection with those violations. But now, barred from using American microchips, software and other components, ZTE struggled to manufacture its telecommunications equipment and smartphones.

Mr. Trump’s tweet on Sunday left many initially scratching their heads, in part because he has regularly trumpeted his efforts to save American jobs.