Japan on Tuesday urged Iran to comply with a U.N. Security Council resolution demanding a suspension of its uranium enrichment, describing it as an important step toward resolving concerns over Tehran's nuclear program.

The resolution, drafted by Britain, France and Germany with U.S. backing and passed Monday, gives Iran until Aug. 31. to halt its enrichment activities or face the threat of economic and diplomatic sanctions.

CountryWatch: Iran

Iran immediately rejected the resolution, saying it would only make negotiations more difficult concerning a package of incentives offered in June for it to suspend enrichment.

"Japan strongly hopes that Iran will accept as early as possible the proposal ... and return to negotiations after complying with the resolution's demands," government spokesman Shinzo Abe told reporters.

Japan imports much of its oil from Iran and has a $2 billion project to tap one of Iran's oil fields in Azadegan -- among the world's largest.

"The Azadegan oil field development project is an extremely important project from the perspective of securing Japan's energy," Abe said. "Economic projects such as the one at Azadegan will not have an impact on our stance toward the nuclear problem."

The U.S. in recent months has asked Tokyo to freeze the project, according to media reports.

Japan has started to curb crude oil imports from Iran amid the nuclear controversy. Oil shipments from Iran fell by 20 percent in April compared to a year earlier, according to Trade Ministry data.