An Iranian exile group says Iran has built an extensive underground tunnel network to hide a secret nuclear weapons program.
The National Council of Resistance of Iran (NCRI) says 14 tunnels house nuclear equipment, research workshops, and command centers across Iran.
The group, which the United States has designated a terrorist organization, urged the International Atomic Energy Agency (IAEA) to take action.
NCRI officials spoke to reporters in London about the tunnels Tuesday, one day before Britain, France and Germany hold new talks with Iran on its nuclear program.
European officials say the talks in Vienna will be "talks about the talks."
European nations have been pressing Iran to abandon its nuclear-fuel program. The United States accuses Iran of secretly trying to develop a nuclear bomb, charges Tehran denies.
Some information for this story provided by AP and Reuters.