RIYADH, Saudi Arabia - A deadly suicide bombing near Islam's second-holiest site in the Saudi city of Medina sparked condemnation across the Muslim world Tuesday, with even the Taliban and Hezbollah denouncing the attack.
Four people were killed in the bombing near the Prophet's Mosque that came as Muslims prepared for this week's Eid al-Fitr festival marking the end of the holy fasting month of Ramadan.
The attack near the mosque -- where the Prophet Mohammed is buried and which attracts millions of pilgrims each year -- was one of three in the Sunni-ruled kingdom on Monday.
There were no claims of responsiblity for the bombings in Medina, Jeddah and the eastern city of Qatif, but the Islamic State group had urged its supporters to carry out attacks during Ramadan.
The Sunni extremists have claimed or been blamed for a wave of shootings and bombings during Ramadan, including in Orlando, Bangladesh, Istanbul and Baghdad.
The Saudi interior ministry said officers became suspicious of a man heading for the mosque through a parking lot.
"As they tried to stop him, he blew himself up with an explosive belt causing his death and the death of four police," it said, adding five others were wounded.
The targeting of Medina caused shock and outrage across Islam's religious divide.
Shiite power Iran called for Muslim unity and the Afghan Taliban branded it "gruesome".
"There are no more red lines left for terrorists to cross. Sunnis, Shiites will both remain victims unless we stand united as one," Iranian Foreign Minister Mohammad Javad Zarif tweeted.
The Taliban said it "condemns this incident in the strongest of terms and considers it an act of enmity and hatred towards Islamic rituals."
Lebanon-based Shiite militant group Hezbollah -- which Riyadh accuses of supporting "terrorist acts" in the region -- also denounced it as "a new sign of the terrorists' contempt for all that Muslims consider sacred."
The United Nations said it was an attack on all Muslims.
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.
"The significance of this attack cannot simply be measured in terms of the four policemen who were reported to have been killed, and the physical damage. It is an attack on the religion itself," said UN rights office spokesman Rupert Colville.
The head of the Saudi Shura Council, Saudi Arabia's main government advisory body, called it "unprecedented".
"This crime, which causes goosebumps, could not have been perpetrated by someone who had an atom of belief in his heart," said Abdullah al-Sheikh.
Cairo-based Al-Azhar, the highest authority in Sunni Islam, stressed "the sanctity of the houses of God, especially the Prophet's Mosque."
Middle East expert Madhawi al-Rasheed said the attack appeared aimed at humiliating Saudi Arabia, the guardian of Islam's holiest sites.
"It's an attempt to actually embarrass the Saudi government because it boasts of protecting the pilgrims and the holy places," said Rasheed, a visiting professor at the National University of Singapore.
Salah al-Budair, the imam of the Prophet's Mosque, warned young people about being lured by the "malignant" ideology of Islamic State.
"(The bomber) is an infidel who has sold himself to the enemies of his religion and his country."
Saudis were rattled by the rare, high-profile attack.
"I apologize 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."
Pakistani behind Jeddah attack
At the same time as the Medina attack, another suicide bombing occurred near a Shiite mosque across the country in the Shiite-populated Gulf city of Qatif.
The interior ministry said "the body parts of three people were found" at the site but had not yet been identified.
Monday's first attack happened in the western Saudi city of Jeddah, where two police officers were wounded in a suicide bombing near the US consulate.
The ministry said the Jeddah attack was carried out by 35-year-old Abdullah Qalzar Khan, a Pakistani who had been living in the city for 12 years.
The US embassy in Riyadh reported no casualties among consulate staff in the attack, which coincided with the US July 4 Independence Day holiday.
Saudi Crown Prince Mohammed bin Nayef bin Abdul-Aziz, the interior minister and anti-terror tsar, said on a visit to wounded policemen in Jeddah that the attacks "will only increase our solidarity and make us stronger" as he 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.
Prince Mohammed has been credited for successfully ending a bombing campaign by al Qaeda in Saudi Arabia between 2003-2006.
Saudi security officials say the Islamic State's supporters inside the kingdom mainly act independently from the group in Iraq and Syria.
Since late 2014 a series of bombings and shootings claimed by IS in Saudi Arabia has targeted minority Shiites as well as members of the security forces, killing dozens.
Most attacks have been in Eastern Province, home to the majority of Shiites in the Gulf state.
IS leader Abu Bakr al-Baghdadi has called for attacks on Saudi Arabia, which is taking part in the US-led coalition bombing the jihadists in Syria and Iraq. The group also considers Shiites to be heretics.
IS spokesman Abu Mohamed al-Adnani had in late May urged the group's supporters to carry out attacks during Ramadan.