TOKYO, July 3 (Reuters) - Nippon Steel's vice chairman plans to return to the United States next week again to discuss its proposed acquisition of U.S. Steel, a company spokesperson said on Wednesday.

The planned visit by Takahiro Mori, the Japanese firm's key negotiator for the deal, follows trips to the U.S. in May and June, highlighting the importance of the $15 billion takeover offer to the world's No. 4 steelmaker.

U.S. Steel's management has backed the bid but the deal faces resistance from the White House and the powerful United Steelworkers (USW) union.

Nippon Steel declined to provide further details of Mori's next visit. According to a source familiar with his travel plans who declined to be identified, Mori will travel to several states where U.S. Steel has operations and meet with local officials, community leaders and workers.

On his last trip, Mori met with U.S. Steel employees and community leaders to gain a better understanding of their views and saw a positive reaction, the company said. (Reporting by Yuka Obayashi and John Geddie; Editing by Edwina Gibbs)