Earlier this month, Japan's biggest bank froze its transactions with Iranian banks following a US court order. The order stemmed from a 2007 federal ruling ordering Iran to make payments to survivors and victims' families of a 1983 bomb attack on a US Marine base in Lebanon, after a federal judge ruled that Iran orchestrated the bombing.
Iran has strongly rejected the accusations, stressing that the West's groundless allegations lack value as they are not corroborated by any substantiating evidence.
The Iranian government has so far not made any payments related to the 2007 ruling, and the order to freeze Iranian assets held in MUFG accounts was part of efforts to secure payment for the damages which have never been proved to have been inflicted by Iran.
The bank, which manages 70-80% of transactions in the country's trade with Iran, filed a complaint to the court over the ruling.