The US accused Iran of harboring al-Qaeda militants and said it was worth checking a claim by an Iranian opposition group that the Islamic government was secretly constructing two uranium enrichment plants.
``We are pressing the Iranians to end their support for terror, including the harboring of al-Qaeda terrorists,'' US presidential spokesman Ari Fleischer said Tuesday.
He described as insufficient the steps that Iran claims to have taken to rein in the terrorist group.
Ruling out force for the time being, Fleischer said the US is addressing the terrorism and nuclear issues through diplomacy.
At the State Department, Secretary of State Colin Powell told reporters that US contacts with Iran will continue.
Iran has turned over some al-Qaeda militants since the Sept. 11 terrorist attacks and has denied that it is harboring any of its members.
That assertion is disputed by US officials. Concern about the link between Iran and al-Qaeda rose sharply after intelligence reports suggested that operatives of the terrorist group in Iran had a role in the May 12 terrorist bombing in Saudi Arabia that killed 34 people, including eight Americans.
Privately, officials said that despite the similarities between Iran and prewar Iraq on both terrorism and weapons, it would be wrong to assume that military action will be used in Iran, just as it was in Iraq.
The National Council of Resistance of Iran (NCRI) said informants inside Iran had made known the existence of two secret uranium enrichment facilities that are under construction about 64km west of Tehran.
A NCRI spokeswoman, Soona Samsami, told a news conference that the facilities will serve as adjuncts of a larger enrichment facility in the city of Natanz. She estimated that Iran could have a nuclear bomb by 2005.
The NCRI has been designated as a foreign terrorist organization by the State Department for years. But it gained some credibility here for having exposed the Natanz facility last August. That disclosure gave greater weight to the administration's claim that Iran is attempting to develop nuclear weapons.
A State Department official said the information was worth checking given the sources that NCRI seems to have in Iran.
Samsami said Iran has been ``showcasing'' a nuclear site at Bushehr to deflect attention from its other nuclear weapons facilities that the NCRI says it is exposing.
The US rejects the assertion the Bushehr facility is for generating electricity. The administration hopes the UN's International Atomic Energy Agency will reinforce American claims about the Iranian program when it visits the country next month.
Iran is a member of the nuclear Non-Proliferation Treaty.
Over vigorous US objections, Russia has been providing technical assistance to the Bushehr project, contending that it is unrelated to nuclear weapons development.
But a Russian Foreign Ministry statement on Tuesday suggested a change in Moscow's thinking. Russia said it has asked Iran to provide guarantees that it is not using its atomic energy program as a cover to develop nuclear weapons.
Meanwhile, Senator Joseph Biden, the senior Democrat on the Senate Foreign Relations Committee, recommended on NBC television a slower approach on Iran so that the administration can focus on military missions in Iraq and Afghanistan.
``I don't think we should be biting off more than we can chew right now,'' Biden said.