TEHRAN, Iran (AP) -- Iran's confirmation Sunday 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.

The United States has sharply 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 had been detained.

It was the first official confirmation, although the student-run ISNA news agency on Friday reported that Shakeri, of Lake Forest, California, was being held and investigated by the security department of the Tehran prosecutor's office.

Shakeri, 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, who is the director of the Middle East program at the Woodrow Wilson International Center for Scholars; Kian Tajbakhsh, an urban planning consultant with George Soros' Open Society Institute; and journalist Parnaz Azima, who works for U.S. funded-Radio Farda...

...The United States has also expressed concern about former FBI agent Robert Levinson, who the United States says has been missing since March after traveling to an Iranian resort island on private business.

Hosseini reiterated Sunday that Iran has no information about Levinson...