US Secretary of State John Kerry has repeatedly called leaders in Saudi Arabia and Iran to try to defuse their diplomatic row, US officials say.
State department spokesman John Kirby said the phone conversations involved foreign ministers of both countries and the Saudi deputy crown prince.
Saudi Arabia cut diplomatic ties with Iran on Sunday after protesters ransacked the Saudi embassy in Tehran.
Protests erupted after Saudi Arabia executed a senior Shia Muslim cleric.
Sunni Muslim Saudi Arabia and Shia Iran are major rivals in the Middle East and back opposing sides in the conflicts in Syria and Yemen.