Saudi Arabia's Foreign Minister Adel al-Jubeir says Iran must stop meddling in Iraq and that the presence of Iranian military units there is "unacceptable."

His comments Sunday come as thousands of Iraqi Shiite militiamen, soldiers and police, backed by Iran, surround the Sunni city of Fallujah ahead of an operation to retake it from the Islamic State group.

Iran says its military advisers in Iraq are there at Baghdad's request to help Iraqi forces fight militants. It has repeatedly rejected Saudi criticisms of its role in the country, instead accusing its regional rival of supporting extremism.

Al-Jubeir, speaking at a press conference with British Foreign Minister Phillip Hammond in Saudi Arabia, said Iran's role had provoked sectarianism among Sunnis and Shiites in Iraq.