Some of the suspects are Iranians and the others are unspecified foreigners, The New York Times reported.
Iran's Intelligence Ministry described those arrested as being involved in a "Zionist-regime-linked" plot to assassinate one of its "specialists." The agency also said it discovered an Israeli spy base in an unspecified neighboring country.
The New York Times said the description appears to link the alleged plot with the killing of Iranian nuclear scientists. At least five have died under mysterious circumstances since 2007.
Few other details of the arrests, which were first announced last week, were reported.