United Nations ? Russian changes to a draft U.N. resolution on Iran’s nuclear program would “cut back substantially” on restrictions the U.S. and its allies are seeking, U.S. Ambassador John Bolton said Monday.

Bolton said Russia specified its proposed changes to the text during a meeting Monday of the five permanent U.N. Security Council members and Germany – the key parties in a standoff with Iran over its nuclear ambitions.

The draft resolution backed by the U.S. and Europe would order all countries to ban the supply of materials and technology that could contribute to Iran’s nuclear and missile programs and impose a travel ban and asset freeze on companies, individuals and organizations that are involved.

But Bolton said the Russian changes would “cut back substantially from the scope” of the lists of suppliers of materials and technology included in the document. He did not elaborate on the differences between the two sides, but said he would consult with Washington about how to proceed before the negotiators’ next meeting Wednesday.

Russia’s U.N. Ambassador Vitaly Churkin said after the meeting that he had presented the U.S. and its allies with “extensive technical answers” to questions they had raised at their last meeting. He sounded optimistic that the negotiations would continue.

“I think the whole purpose of this exercise is to better understand where we all are coming from,” he said.

Russia is building Iran’s first nuclear power plant and strongly supports Iran’s right to nuclear energy, but has joined the U.S. and Europe in demanding it halt enrichment in order to ease concerns that Tehran is seeking to develop nuclear weapons.

However, Moscow has rejected the European draft, saying the sanctions are too broad and too strong, and urged revisions including the removal of all references to the plant Russia is building in the Iranian city of Bushehr.

In Washington, President Bush warned Iran it will face “economic isolation” if it presses ahead with its nuclear program.

“There has to be a consequence for their intransigence,” Bush told reporters after he discussed Iran with Israeli Prime Minister Ehud Olmert at a meeting Monday. “I recognize the threat to world peace that the Iranians … pose, as does the prime minister,” Bush added.

Russia and China, which also has major commercial ties with Iran, have publicly pushed for dialogue instead of U.N. punishment despite the collapse last month of a European Union attempt to entice Iran into talks.

China’s U.N. Ambassador Wang Guangya said Monday the latest discussions centered on a number of “key, difficult issues,” but he described the mood as nonconfrontational.

Last week, Wang had offered a more dire assessment, saying there were many areas of differences among the parties that could not be bridged.

Iran’s top nuclear negotiator, Ali Larijani, met with Russian President Vladimir Putin and other Russian officials during the weekend in Moscow to discuss the nuclear standoff.

Larijani remained defiant after the first round of meetings Friday, saying Tehran would push ahead with its nuclear program. He did not speak to the media afterward, but Russian officials said they believed talks with Iran still were possible.