The U.S. and its allies hoped to secure Iran's approval Friday for a proposed deal that would ship most of the country's uranium abroad for enrichment and ease Western fears about Iran's potential to make a nuclear weapon.

Approval of the draft agreement would be a key victory for President Obama, who has stepped up diplomatic engagement with Iran since he took office in January and faulted the Bush administration for refusing to talk to U.S. adversaries.

But Iran's endorsement of the proposal, which calls for shipping low-enriched uranium to Russia for further enrichment to a level suitable as fuel for a research reactor — but not for nuclear weapons, is far from certain.

Iran's deputy parliament speaker, Mohammad Reza Bahonar, dismissed the plan Thursday, the first public reaction in Tehran to the proposal.

Iran's parliament will not vote on the draft plan, and Bahonar does not speak for the government, which is to decide the matter. But it's unclear if his comments reflect high-level resistance to the deal or the opinions of some influential politicians in Iran.

The proposal may meet resistance by some Iranian leaders because it weakens Iran's control over its stockpiles of nuclear fuel and could be perceived as a concession to the U.S., which suspects Iran is using its nuclear program as a way to covertly develop weapons — an allegation denied by Tehran.

The draft agreement was formalized Wednesday after three days of talks in Vienna between Iran and world powers, including the U.S. The talks followed a similar meeting at the beginning of October in Geneva that included the highest-level bilateral contact between the U.S. and Iran in years.

The head of the U.N. nuclear watchdog, Mohamed ElBaradei, said after the completion of the Vienna talks that he hoped Iran and its three interlocutors — the U.S., Russia and France — would approve the plan by Friday.

Russia was the first to heed that call, with Foreign Minister Sergey Lavrov saying Friday he hopes the other nations involved will follow in endorsing the agreement sponsored by the International Atomic Energy Agency.

"We expect not only Iran but other countries involved in the plan proposed by the IAEA to confirm their acceptance of that project," he said.

In Washington, State Department spokesman Ian Kelly said Thursday that while some in Iran may disagree with the proposal, the U.S. government was waiting to hear the government's "authoritative answer" Friday.

Failure to endorse the deal could prompt the U.S. to push for harsher international sanctions against Iran. The U.N. Security Council has already passed three sets of sanctions against Iran for failing to suspend uranium enrichment, but the U.S. faces a serious challenge in convincing Russia and China to go even further because of their close ties to Tehran.

Under the Vienna-brokered plan, Iran is required to send 1.2 tons of low-enriched uranium — around 70 percent of its stockpile — to Russia in one batch by the end of the year, French Foreign Ministry spokesman Bernard Valero said Thursday.

After further enrichment in Russia, France would convert the uranium into fuel rods that would be returned to Iran for use in an aging reactor in Tehran used for medical research, he said.

Iran needs 20 percent-enriched uranium for its Tehran plant, which has been producing radioisotopes for medical purposes over the past decades.

The country is currently producing fuel at a 3.5 percent enrichment rate for a nuclear power plant it is planning to build in southwestern Iran. Iranian officials have said it is more economical to purchase the more highly-enriched uranium needed for the research reactor than produce it domestically.

Iran agreeing to ship most of its enriched uranium abroad would significantly ease fears about Tehran's nuclear program, since 2,205 pounds is the commonly accepted amount of low-enriched uranium needed to produce weapons-grade uranium for a single nuclear bomb.

Based on the present Iranian stockpile, the U.S. has estimated that Tehran could produce a nuclear weapon between 2010 and 2015, an assessment that broadly matches those from Israel and other nations.

But David Albright of the Washington-based Institute for Science and International Security, which has tracked Iran for signs of covert proliferation, has said the deal would buy only a limited amount of time. He has said Tehran could replace the amount of enriched uranium shipped abroad "in a little over a year."

Former U.N. chief weapons inspector Hans Blix also cautioned against viewing the deal as a total solution

"The Iranians are certainly not agreeing to stop enrichment next year," said Blix during a speech Thursday at the University of Arkansas' Clinton School of Public Service. "Therefore, I think it would be a good sign, a positive sign that you could have agreements, but it does not really solve the major problem."