Iranian media reports say authorities have arrested 40 people suspected of plotting an attack against military installations in the country's restive southeast, near the border with Pakistan.
Iran's official IRNA news agency reported that those arrested belonged to a "terrorist group," but did not name the group.
IRNA quoted Interior Minister Abdolreza Rahmani Fazli as saying that those arrested had built a tunnel, which they had planned to use for "carrying out attacks and militant activities."
Earlier this month, four Iranian border guards were killed near the Pakistani border.
Iran's southeastern province of Sistan-Baluchistan, which borders Pakistan and Afghanistan, has been the scene of deadly fighting in recent weeks between Iranian border guards and militants.