The United Nations nuclear watchdog, the International Atomic Energy Agency, is expected to issue its most detailed report yet on research in Iran seen as geared to developing nuclear weapons.
Iranian officials have already seen the Vienna-based IAEA's intelligence to be released to the UN this week, diplomats told the AFP news agency.
In a report on its website, the Washington Post newspaper quoted Western officials as saying that the new information reinforced concerns that Iran continued to conduct weapons-related research after 2003 when, according to US intelligence agencies, Iranian leaders halted such experiments in response to international and domestic pressures.
Intelligence suggests Iran also received assistance from foreign scientists to overcome key technical hurdles, including a former Soviet weapons scientist who tutored Iranians on building high-precision detonators necessary to trigger a nuclear chain reaction, the newspaper reported.
In the run-up to the report's release, Israeli President Shimon Peres said the likelihood that of a military attack to stop Iran from obtaining nuclear weapons was "now closer to being applied than the application of a diplomatic option".
But Sergei Lavrov, Russia's foreign minister, said on Monday that any military strike against Iran would be "a very serious mistake fraught with unpredictable consequences".
Some experts believe Israel could launch a strike if it is convinced that the West is not prepared to take stronger steps against a nuclear Iran.
Iran insists its nuclear programme is only for peaceful purposes and says it will respond to any attacks by striking at Israeli and US interests in the region.
Ex-state department spokesperson PJ Crowley speaks on Iran
Meanwhile the White House said it expects the pending report on Iran's nuclear capabilities to echo US concerns about Iran's behaviour and its failure to live up to its international obligations.
However, Jay Carney, the White House spokesman, would not address the specific findings of the upcoming IAEA report.
Carney said the US continues to focus on using diplomatic channels to pressure Iran to abandon its nuclear program. But he says that the US continues to keep all options open when it comes to dealing with Iran.
Ali Akbar Salehi, the Iranian foreign minister, said in comments published in Iran on Sunday that suggestions it had continued to conduct weapons research were based on "counterfeit" claims.
Iranian President Mahmoud Ahmadinejad said on Monday that the US feared Iran's growing military power because it was now able to compete with Israel and the West.
"Yes, we have military capabilities that are different from any other country in the region," Ahmadinejad said in comments reported by in Egypt's Al-Akhbar newspaper.
"Iran is increasing in capability and advancement and therefore we are able to compete with Israel and the West and especially the United States. The US fears Iran's capability. Iran will not permit [anyone from making] a move against it."
Ahmadinejad said that it was Israel that possessed nuclear warheads while Iran only wanted to nuclear capability for peaceful means.
Source: Al Jazeera and agencies