Those lobbying efforts have so far failed. The European Union will not cancel or delay the embargo on Iranian oil tankers, EU Energy Commissioner Guenther Oettinger said at an industry conference on Wednesday.
The International Energy Agency said on Tuesday that Iran's crude exports in April and May have fallen by 1 million bpd since the end of 2011 to 1.5 million bpd and that Tehran may need to shut in production.
China, Japan, India and South Korea have cut purchases by about a fifth from the 1.45 million bpd they were buying a year ago ahead of the imposition of the sanctions.
It is the first time Japan has sought to provide guarantees on marine shipments, said an official in the country's transport ministry, which is sponsoring the legislation. The official, who helped draft the bill, said he didn't know when the law will be passed by parliament.