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The US is mulling harsh sanctions on Iran by the end of this year if Tehran does not curb its nuclear program, according to news reports.

The reports came as hard-line Iranian President Mahmoud Ahmadinejad was formally endorsed for a second term by Supreme Leader Ayatollah Ali Khamenei in a ceremony Monday boycotted by leading opposition figures who dismissed the election result as a sham, reports Reuters.

The BBC said the US had already consulted on the sanctions plan with Israel and its European allies. The sanctions under consideration would bar shipments of refined petroleum products and byproducts to Iran, put restrictions on the purchase of Iranian gas and oil, and tighten rules on investments in Iran's oil industry.

Such an embargo could be a serious blow to Iran's economy, since it has little refining capability of its own. But the sanctions would require cooperation from China and Russia to be effective.

The timetable is for an assessment to be made of Iran's intentions in the last week of September, when world leaders always gather in New York for the annual meeting of the UN General Assembly. There would also be discussions at a G20 summit in Pittsburgh the same week.

If Iran continued to resist freezing its enrichment activities and failed to agree to discuss its nuclear program, then sanctions would be imposed, or at least realistically threatened, by the end of this year.

Meanwhile, The Times of London reported Monday that Iran could build a nuclear bomb within a year, citing anonymous "Western intelligence sources." The sources told The Times that such a project could be initiated at any time, on an order from Ayatollah Khamenei.

"If the Supreme Leader takes the decision [to build a bomb], we assess they have to enrich low-enriched uranium to highly-enriched uranium at the Natanz plant, which could take six months, depending on how many centrifuges are operating. We don't know if the decision was made yet," said the intelligence sources.

Another six months would be needed to assemble a warhead, the article said.

According to the intelligence sources, an Iranian nuclear weapons research program was indeed halted in 2003, as has been widely reported. But that, said the Times' sources, was because it achieved its goal: Iranian scientists successfully created a method to weaponize uranium, giving them the ability to make a nuclear warhead that could be fit atop its long-range missiles. (Click here for a 2005 map of Iranian nuclear facilities from the Carnegie Endowment.)

However, the Times assessment differs significantly from three major reports this year: one by the US Senate Foreign Relations Committee (PDF), a joint assessment by Russian and American scientists, and a report by RAND Corp. A Christian Science Monitor briefing on Iran's nuclear program, published in June and based on these reports, notes that while it would take only a year for Iran to develop a simple nuclear device, it would take six to eight years to develop a nuclear bomb that could be delivered by ballistic missile.

In a report in June, the International Crisis Group said Iran will not compromise on its right to enrich uranium, and that it most wants the US to "change the way it sees and treats Iran."

The group noted that economic sanctions had already hurt Iran, but that such sanctions were "highly unlikely to produce meaningful policy shifts," because "Iran's decision-making on core strategic issues is only marginally affected by economic considerations." Indeed, the leadership in Tehran actually benefits from tensions with the United States, the group said.

Hostility toward the U.S. is one of its ideological pillars; economic adversity can be blamed on sanctions, while technological success – notably in the nuclear field – can be hailed as a powerful symbol of resistance against Western powers. The greater tensions are with Washington, the easier it is for the regime to rally supporters, suppress dissent and invoke national unity against a common enemy.