"We don't know if the recent rally in the iron ore market will be short-lived or will lead to a structural change of the market for the long term," Japan Iron and Steel Federation Chairman Koji Kakigi told a news conference.

Kakigi, who is also president of JFE Steel, a unit of JFE Holdings, said his company buys about 20 percent of its iron ore from Vale, and supplies have not been affected so far.

(Reporting by Yuka Obayashi; editing by Darren Schuettler)