"This new claim by the US government ... is so baseless and ridiculous that it is not really worth answering," said Foreign Ministry spokesman Saeed Khatibzadeh.
A Justice Department indictment unsealed on Tuesday showed that US prosecutors have charged four Iranians, alleged to be intelligence operatives for Tehran, with plotting to kidnap the activist. The indictment did not name the target of the plot, but Reuters has confirmed that she is Iranian-American journalist Masih Alinejad.