By Jonathan Head
BBC News, Tokyo
Iranian Foreign Minister Manouchehr Mottaki has arrived in Tokyo for talks about Iran's nuclear programme.
Manuchehr Mottaki was once Iran's ambassador to Tokyo
Japan, which imports much of its oil from Iran, is hoping to persuade the Iranian government to abandon its nuclear enrichment programme.
Tokyo wants Tehran to accept the offer to have its nuclear fuel reprocessed by Russia.
Mr Mottaki is due to meet his Japanese counterpart Taro Aso and Prime Minister Junichiro Koizumi during his visit.
Two years ago Japan did something it rarely does - it defied pressure from its closest ally, the United States, and signed a deal with the Iranian national oil company under which they would jointly develop the massive Azadegan oil field.
Iran needs more foreign investment and Japan needs oil. Iran currently provides one-sixth of Japan's oil imports.
So the crisis over Iran's nuclear programme has put Japan in an awkward position, made worse by intense competition with China for access to energy reserves.
China is in the process of finalising its own agreement with Iran to develop another large oil field.
If Iran refuses to abandon its nuclear fuel enrichment programme, and is punished by the UN Security Council, Japan may find it impossible to resist US demands that it pull out of the Azadegan project.
Foreign Minister Taro Aso has said he hopes to persuade his Iranian counterpart to be more receptive to the concerns of the international community.
And he may be helped a little, not just by Japan's traditionally good relations with the government in Tehran, but also by the fact that Manouchehr Mottaki once served as Iran's ambassador to Tokyo in the 1990s.