Israeli PM Ehud Olmert has insisted Iran's nuclear programme remains dangerous, and called on world powers to prevent it acquiring atomic weapons.
Israel is said to be the only nuclear-armed state in the Middle East
Mr Olmert said Iran had no need to "act with frenzied haste" to enrich uranium unless it wanted to develop weapons.
His comments came a week after a US intelligence report said Iran halted its nuclear weapons programme in 2003.
Tehran, which has always insisted its nuclear programme is solely for peaceful purposes, welcomed the report.
Earlier, an Iranian opposition group based in Paris said Iran had halted its nuclear weapons programme four years ago, but then restarted it in 2004 after moving equipment to several sites to avoid detection.
The National Council of Resistance of Iran (NCRI), which first exposed Iran's nuclear programme in 2002, said its sources reported that Tehran was leaking false information to Western intelligence services through double agents.
"We announce vehemently that the clerical regime is currently continuing its drive to obtain nuclear weapons," NCRI spokesman Mohammad Mohaddessin told a news conference in Brussels.
The France-based group is the political wing of the Mojahedin-e Khalq Organisation (MKO), an Iranian armed resistance group which has been labelled as "terrorist" by the US and European Union.
In a speech at Israel's Institute for National Security Studies, the Israeli prime minister said last week's US National Intelligence Estimate (NIE) on Iran should not prompt a reduction in international pressure on the country to halt its uranium enrichment activities.
The US and its European allies on the UN Security Council have been pushing for tougher UN sanctions, but Russia and China have said the report raises questions about the need for new measures.
Mr Olmert said Iran continued to develop dangerous ballistic missiles
"Iran continues its activities to enrich uranium, and even according to the NIE report, it is likely to accumulate sufficient amounts to create a nuclear weapon by 2010," Mr Olmert said.
"Iran was, and remains dangerous, and we must continue international pressure with full force to dissuade Iran from nuclear tendencies."
Mr Olmert said that while continuing to produce enriched uranium - which can be used as the basis of a nuclear bomb - the Islamic republic was also developing sophisticated electrical systems and ballistic missiles.
He added that Iran had no need for electricity produced by nuclear power, did not have the infrastructure to create energy for civilian purposes, and had no need to act with "frenzied haste" to create enriched uranium unless it wanted to develop nuclear weapons.
Mr Olmert also praised US President George W Bush for declaring that the NIE report still did not detract from the danger Iran posed to the world and that he would continue to push for a third UN sanctions resolution.
"I trust and am confident that the United States will continue to lead the international campaign to stop the development of a nuclear Iran," he said.
Israel, widely believed to be the only nuclear-armed state in the Middle East, says repeated statements by Iran's president that the Jewish state should cease to exist are evidence of an intention to use nuclear weapons against it in the future.