Iran's intelligence ministry said Monday it had thwarted a major plot to carry out bomb attacks in the capital Tehran and other parts of the country, state media reported.
"One of the biggest takfiri-Wahhabi terrorist plots was discovered and foiled," the official IRNA news agency quoted the ministry as saying, using terms applied by Iran to Sunni extremist groups.
"A series of bomb attacks prepared in various areas deep inside the country and especially in Tehran and some other provinces... were foiled, the terrorists were arrested and a number of ready-made bombs were recovered," it said.
No more details were provided. The ministry said more information would come following investigations "both inside and outside the country."
The secretary of Iran's Supreme National Security Council, Ali Shamkhani, told the ISNA news agency the plot included plans for "suicide attacks in Tehran".
Iran has been helping both the governments of Iraq and Bashar al-Assad's regime in Syria.
Iranian cities have not however faced any serious threat of terrorist attack.
An increased police presence in Tehran in November and December -- with armed security forces guarding subway stations and other public areas in Tehran -- raised concerns that an attack was possible.
But the capital's police chief, Hossein Sajedinia, said the presence was only part of "counter-terrorism drills".
Iranian forces clashed with militants last week on the country's northwestern and southeastern borders, leaving several dead.
The elite Revolutionary Guards killed 12 Kurdish rebels in fighting near the Iraqi border on Wednesday that also left three members of the Guards dead.
Police said the rebels were members of the Party of Free Life of Kurdistan (PJAK), an Iranian Kurdish group with close links to the terrorist group PKK.
The same day, state television reported that a police officer and five members of militant group Jaish-ul Adl had been killed in clashes in the southeastern Sistan-Baluchistan province.