TEHRAN: Iran on Tuesday condemned three suicide bombings that rocked its regional rival Saudi Arabia, one of them targeting Masjid-i-Nabvi (PBUH), Islam's second holiest place, in Madinah.

"There are no more red lines left for terrorists to cross. Sunnis and Shias will both remain victims unless we stand united as one," Iranian Foreign Minister Mohammad Javad Zarif said on Twitter.

Four security guards were killed in the Madinah bombing.

The other attacks on Monday targeted the United States consulate in the Red Sea city of Jeddah and a Shia mosque in Saudi's Qatif.

"Terrorism knows no border or nationality and there is no solution except creating an international and regional unity against this phenomenon," foreign ministry spokesman Bahram Ghasemi told state broadcaster IRIB.

There were no immediate claims of responsibility for the attack on Masjid-i-Nabvi (PBUH).

Iran and Saudi Arabia are locked in an increasingly tense competition for regional influence, and back opposing sides in regional conflicts, including in Syria and Yemen.

Riyadh broke off diplomatic relations with Tehran in January after protesters attacked its embassy in the Iranian capital following the execution of a Shia cleric, and its consulate in Mashhad.