Japan's Nippon Steel is committed to its $15 billion acquisition of U.S. Steel and is confident of completing it by year-end, a senior executive has said, despite strong U.S. opposition including from President-elect Donald Trump.

"We will not give up on the deal. ... There is no global strategy without the U.S.," Nippon Steel Vice Chairman Takahiro Mori said this week, after returning from his eighth visit to the United States since the deal was announced a year ago.

With U.S. Steel, Nippon Steel aims to raise its global steel production capacity to 85 million metric tons per year from 65 million tons now and the asset is core to its goal of lifting production capacity to more than 100 million tons in the long-term.