Iran's official IRNA news agency says authorities have arrested 40 suspects linked to the discovery of an underground tunnel in the country's far east, near the Pakistani border.

Thursday's report says those arrested belong to a "terrorist group" but doesn't identify the group. It quotes Interior Minister Abdolreza Rahmani Fazli as saying the subterranean tunnel discovered two nights ago was meant for "carrying out attacks and militant activities."

Earlier in July, four Iranian border guards were killed by gunmen near the Pakistani border. Security forces have also occasionally clashed with militants groups in the area believed to be affiliated with al-Qaida and which have claimed responsibility for several attacks in the past years.

Most of the violence is focused in Iran's eastern Sistan-Baluchistan province, which borders Pakistan's southwestern Baluchistan province.