"We have no choice but to return to the United Nations Security Council," French Foreign Minister Philippe Douste-Blazy said after talks with his counterparts from the United States, Britain, Russia, China and Germany.

Expressing "profound disappointment," the six nations said they would seek a resolution at the Security Council requiring Iran to suspend uranium enrichment.

The six nations had called on Iran to respond positively to its offer by Wednesday's deadline. But hopes of a breakthrough were dashed when talks in Brussels between EU and Iranian officials failed to yield results.

The five permanent Security Council members plus Germany had offered economic and trade incentives as well as access to peaceful nuclear technology in exchange for a pledge by Iran to suspend uranium enrichment activities during talks over its nuclear programs.

They had hoped for a response before the G8 summit of industrialized nations in St. Petersburg, Russia, this weekend. But Tehran insisted it would not respond formally to the offer until August.

Speaking after Tuesday's talks, Iran's top nuclear negotiator Ali Larijani urged patience.

"We have to go into a long process, we must be patient and do everything exactly," he told reporters.

But the six foreign ministers said they were not prepared to give Tehran the benefit of the doubt.

"The Iranians have given absolutely no indication of their readiness to seriously discuss the substance of our proposal," Douste-Blazy told reporters.

He said the Security Council would seek to force Iran to suspend its uranium enrichment program.

"Should Iran refuse to comply then we will work for the adoption of measures under article 41 of Chapter VII of the U.N. charter," he added.

Under article 41, the Security Council could ask United Nations members to endorse economic or other sanctions against Iran but could not seek to apply military force.

In the short statement released by the ministers, they said that the Security Council action could be halted at any time should Iran decide to accept the conditions for negotiations.

Concern has been mounting about Iran's nuclear ambitions since it emerged in 2003 that the Islamic Republic had been operating a uranium enrichment program in secret for 18 years. Britain, France and Germany -- the so-called EU Three -- held talks with Tehran aimed at ensuring its nuclear programs were peaceful; however these collapsed last summer.

The stand-off escalated sharply in January when Iran removed United Nations seals from three nuclear facilities, ending a two-year suspension of uranium enrichment-related activities. Iran was referred to the Security Council in March but the process was suspended in order to formulate the incentive offer, largely at the behest of Russia and China which are reluctant to impose any form of sanctions.

Under the nuclear non-proliferation treaty, countries are allowed to enrich uranium for peaceful nuclear energy purposes; this, Iran maintains, is its only intention.

However, the same technology can be used to create nuclear weapons, which some countries, notably the United States and Israel, fear is Tehran's true objective.

Any attempt to impose sanctions on Iran could be thwarted by resistance from Security Council veto-holders Russia and China, both of which have key interests in the country. Russia has a $1 billion contract to build Iran's first atomic reactor at Bushehr, while China is heavily reliant on Iranian oil exports for its energy supplies.

The contents of the incentive package have not been made public but it is understood to include provision of light water nuclear reactors and enriched fuel, access to U.S. agricultural and civilian aircraft technology and support for Iranian membership of World Trade Organization.

If Tehran does accept the offer it would open the way for the first high-level talks between Iranian and U.S. officials since the Iranian hostage crisis in 1979.

The stakes could hardly be higher. U.S. President George W. Bush has made clear that the use of force against Iran remains an option, while Iranian Supreme Leader Ayatollah Ali Khamanei warned last month that the country could disrupt shipments of oil from the Gulf if the United States made a "wrong move" in the dispute. Iran has also suggested it could use its influence to stir up trouble in the region, particularly in neighboring Iraq.

Related Links
Learn about missile defense at SpaceWar.com