WASHINGTON — Senator Lieberman said yesterday that the American government should consider a military strike against Iran because of Tehran’s involvement in Iraq.

“I think we’ve got to be prepared to take aggressive military action against the Iranians to stop them from killing Americans in Iraq,” Mr. Lieberman said. “And to me, that would include a strike over the border into Iran, where we have good evidence that they have a base at which they are training these people coming back into Iraq to kill our soldiers.”

The American government accuses Iran of fostering terrorism, and Tehran’s nuclear ambitions have brought about international reproach.

Mr. Lieberman, the Democratic nominee for vice president in 2000 who now represents Connecticut as an independent, spoke of Iranians’ role in the continued violence in Iraq.

“We’ve said so publicly that the Iranians have a base in Iran at which they are training Iraqis who are coming in and killing Americans. By some estimates, they have killed as many as 200 American soldiers,” Mr. Lieberman said. “Well, we can tell them we want them to stop that. But if there’s any hope of the Iranians living according to the international rule of law and stopping, for instance, their nuclear weapons development, we can’t just talk to them.”

Democratic presidential hopeful Bill Richardson said tough negotiation is called for.

“I would talk to them, but I would build an international coalition that would promote and push economic sanctions on them,” Mr. Richardson said. “Sanctions would work on Iran. They are susceptible to disinvestment policy. They are susceptible to cuts, economic sanctions in commodities.”

In related news, Iran’s confirmation yesterday that it has detained a fourth Iranian-American — this one a peace activist from California — seems certain to further rile relations between the two countries, already tense over Iran’s nuclear program. America has criticized the detentions but Iran insists America has no right to interfere.

Mohammad Ali Hosseini, the spokesman for Iran’s foreign ministry, confirmed at his weekly news briefing that Iranian-American Ali Shakeri is being held.

On Friday, the semi-official ISNA news agency first reported the detention and investigation of Mr. Shakeri, of Lake Forest, Calif., by the security department of the Tehran prosecutor’s office.

Mr. Shakeri, a founding board member of the University of California, Irvine, Center for Citizen Peacebuilding, is the fourth dual citizen detained in Iran in recent months.

Iranian officials previously confirmed the detentions of three other Iranian-Americans: scholar Haleh Esfandiari, the director of the Middle East program at the Woodrow Wilson International Center for Scholars; Kian Tajbakhsh, an urban planning consultant with George Soros’s Open Society Institute, and Parnaz Azima, a journalist who works for the American-funded Radio Farda.

All three are accused of endangering Iran’s national security and of espionage, according to a judiciary spokesman. It is not known if Mr. Shakeri has been accused of specific wrongdoing.