Nuclear talks between Iran and major world powers was at a difficult moment, visiting U.S. under Secretary of State Wendy Sherman said here.

"I don't believe they (the talks) have failed, but they are at a difficult moment," Sherman told Interfax news agency in an interview published Friday.

The P5+1 group, including Britain, China, France, Russia, the United States and Germany, had taken basic confidence-building steps for the nuclear talks, and Iran should come back to the negotiating table "with far greater seriousness of purpose," the U.S. official said.

The P5+1 proposals, which could be summarized as "stop, shut and ship," called for Iran to stop enriching uranium up to 20 percent, close its nuclear facilities and take the already 20-percent-enriched uranium out of the country.

Iran, in response, said it would temporarily halt its 20 percent enrichment in exchange for a lift of all sanctions against it, according to the diplomat.

Calling such a demand an "unreasonable non-starter," Sherman urged Iran to resume talks with world powers to avoid further isolation.

"They would see continued sanctions and sanction enforcement, and there will be great consequences for them," she said.

If Iran was ready to make agreements under the framework of the P5+1 mechanism and in accordance with the UN Security Council resolutions, the United States "is absolutely ready to support such an agreement," Sherman said.

Meanwhile, the U.S. government was trying to convince Israel that a diplomatic solution toward the Iranian nuclear program was possible, the official said.

At the same time, the U.S. side understood "Israel will have to make a decision that is best for their own future and their sovereign decision-making process," Sherman said.