"To the extent that pressure will continue to be brought on oil producing nations we will continue to have a distorted market," Ramirez said ahead of a meeting of OPEC ministers in Vienna on Monday and Tuesday.

"The pressures on Iran are unacceptable and will definitely result in greater tension on the oil market," he said. "The invasion of Iraq is a good example of this."

Iran is OPEC's second biggest producer of crude oil after Saudi Arabia.

Ministers from the Organisation of Petroleum Exporting Countries are expected to raise official production by the cartel, which accounts for about 40 percent of world oil output, by 500,000 barrels a day to 28.5 million bpd to help ease oil prices that hit record highs in late August.

Iran has come under pressure to give up a nuclear fuel programme that Tehran insists is for peaceful purposes but which has raised concerns in the United States and European Union about its potential for producing nuclear weapons.

The United Nations' atomic energy watchdog was to meet Monday amid a clash between the West and Iran over Tehran's insistence on continuing nuclear fuel work, with a growing possibility of the issue being referred to the UN Security Council.

The United States and EU want the International Atomic Energy Agencyto bring Iran before the Security Council, which could adopt resolutions or apply trade sanctions to try and convince Tehran to halt nuclear fuel cycle work.

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