The UN human rights chief on Tuesday called a suicide bombing outside the Prophet Mohammad's Mosque in the Saudi city of Madinah an attack on Islam itself and many Muslims expressed shock that their second-holiest site had been targeted.
Three apparently coordinated suicide attacks on Monday targeted Madinah, the US consulate in Jeddah and the largely Shi'ite Muslim city of Qatif on Monday. At least four security officers were killed.
No group has claimed responsibility but ISIL has carried out similar bombings in the US-allied kingdom in the past year, targeting Shi'ites and Saudi security forces.
Zeid Ra'ad al-Hussein, the UN High Commissioner for Human Rights and a member of the Jordanian royal family, delivered his remarks via a spokesman in Geneva.
"This is one of the holiest sites in Islam, and for such an attack to take place there, during Ramadan, can be considered a direct attack on Muslims all across the world," he said, referring to the Islamic holy month.
"It is an attack on the religion itself."
Militant attacks on Medina are unprecedented. The city is home to the second-holiest site in Islam, a mosque built by the Prophet Mohammed, the founder of Islam, which also houses his tomb.
Attacks on Makkah, the most sacred place in Islam, have also been extremely rare. The Al Saud ruling family considers itself the protectors of both sites. ISIL says the Saudi rulers are apostates and has declared its intention to topple them.
Saudis were rattled by the rare, high-profile attack.
"I apologise to everyone if I don't congratulate you this Eid," Khaled bin Saleh al-Shathri, a Saudi businessman, wrote on Twitter.
"I am shocked by the deaths of five of my brothers and the wounding of four others as they guarded the holiest places."
Iran also 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.
"The security of the homeland is good, it is at its highest levels and thanks be to God it gets stronger every day," the state news agency SPA quoted him as saying during a visit to some of the wounded in the Jeddah attack.
Prince Mohammed has been credited for successfully ending a bombing campaign by al Qaeda in Saudi Arabia between 2003-2006.
Monday's bombings came days before the end of the holy month of Ramadan when Muslims fast from dawn until dusk.
Saudi security officials say the ISIL's supporters inside the kingdom mainly act independently from the group in Iraq and Syria.
Salah al-Budair, the imam of the Prophet's Mosque, warned young people about being lured by the "malignant" ideology of ISIL.
"(The bomber) is an infidel who has sold himself to the enemies of his religion and his country."For all the latest business news from the UAE and Gulf countries, follow us on Twitter and Linkedin, like us on Facebook and subscribe to our YouTube page, which is updated daily.