TOKYO - Japan will make efforts to gain U.S. understanding for a plan to develop Iran's massive Azadegan oil field, the trade minister said.

Japan must explain to the United States Tokyo's stance on energy issues and strive to make things go in a better direction, Economy, Trade and Industry Minister Takeo Hiranuma told a news conference on Friday.

The comment came a day after a cautious remark about the deal, estimated to be worth more than two billion dollars, by a top foreign ministry official.

"I do not think we can sign the deal on the Azadegan oil field, at least at the moment, although we have to make a conclusion after seeing future developments," Senior Vice Foreign Minister Toshimitsu Motegi told reporters.

Washington is opposed to the planned Japanese investment.

State Department spokesman Richard Boucher said in a statement earlier this week the department "would be opposed to such investment at any time.

"This would be a particularly unfortunate time," he said, warning of possible sanctions if the deal goes ahead.

Japan and Iran agreed in 2000 to start negotiations over the oil field.

U.S. Congress has passed a legislation known as D’Amato Law which says those companies which invest more than 40 million dollars in Iranian oil industry will face U.S. sanctions.

The Japanese consortium includes trading house Tomen Corp., Inpex Corp., and Japan Petroleum Exploration Co.

Iranian Foreign Minister Kamal Kharazi told reporters on Wednesday that Japanese companies "can of course continue their negotiations" but would no longer be given exclusive signing privileges.

"Others can also take part in the negotiations," the minister said.