The king of Saudi Arabia is warning his country will strike with an "iron hand" against people who preyed on youth vulnerable to religious extremism, a day after suicide bombers struck three cities in an apparently coordinated campaign of attacks.
In a speech marking Eid al-Fitr, the holiday that celebrates the end of the Islamic holy month of Ramadan, King Salman said a major challenge facing Saudi Arabia was preserving hope for youth who faced the risk of radicalisation.
Four security officers were killed in Monday's attacks that targeted US diplomats, Shi'ite Muslim worshippers and a security headquarters at a mosque in the holy city of Medina.
The UN human rights chief on Tuesday described the bombing outside the Prophet Mohammed's Mosque in Medina as "an attack on Islam itself" and many Muslims expressed shock that their second-holiest site had been targeted.
No group has claimed responsibility but Islamic State militants have carried out similar bombings in the US-allied, Sunni Muslim-ruled kingdom in the past year, targeting minority Shi'ites and Saudi security forces.
Militant attacks on Medina are unprecedented.
The city is home to the second most sacred site in Islam, a mosque built in the 7th century by the Prophet Mohammed, the founder of Islam, which also houses his tomb.
Attacks on Mecca, the holiest place in Islam, have been extremely rare.
The Al Saud ruling family considers itself the protectors of both sites.
IS says the Saudi rulers are apostates and has declared its intention to topple them.
Iran, the region's major Shi'ite power, condemned the attacks.
Saudi Arabia's crown prince and anti-terror tsar, Mohammed bin Nayef bin Abdul-Aziz, sought on Tuesday to reassure Saudis of the country's security.
Prince Mohammed has been credited for ending a bombing campaign by al-Qaeda in Saudi Arabia between 2003 and 2006.
Saudi security officials say IS supporters inside the kingdom mainly act independently from the group in Iraq and Syria, its main areas of operations.
Salah al-Budair, the imam of the Prophet's Mosque, warned young people about being lured by the "malignant" ideology of IS.
"(The bomber) is an infidel who has sold himself to the enemies of his religion and his country," he said.
