Japan has called on Iran to end its nuclear activities after its close trading partner defied Western pressure and announced an end to a two-year suspension on uranium enrichment.
"Japan deems it a matter of deep regret," foreign ministry press secretary Yoshinori Katori said in a statement released late on Tuesday.
"Japan strongly calls on Iran to immediately cease the resumption of the research and development activities" related to uranium enrichment and reprocessing, Katori said.
He called on Iran to comply with International Atomic Energy Agency resolutions "including the suspension of all the uranium enrichment-related and reprocessing activities without exception."
Iran on Tuesday removed the seals from its nuclear facilities and resumed research activities. The Islamic republic had suspended its work in 2003 in exchange for economic and other incentives from Britain, France and Germany.
Japan, which is almost entirely dependent on imported energy to fuel its massive economy, has forged close commercial links with Iran despite concern by the United States, Tokyo's main ally.