RIYADH: Outrage spread on Tuesday after a deadly suicide bombing at Islam's second-holiest site in the Saudi city of Medina, one of three attacks in the kingdom on a single day.

Religious and political leaders across the Middle East denounced the attack near the Prophet's (PBUH) Mosque that left four dead and came as Muslims prepare for the feast this week marking the end of the holy month Ramazan.

There were no claims of responsibility for Monday's bombings in Medina, Jeddah and the eastern city of Qatif.

The suicide bombing in Medina came during sunset prayers at the mosque — where Prophet Muhammed (PBUH) is buried and which attracts millions of pilgrims each year.

The targeting of Madinah caused widespread outrage, both in Saudi Arabia and across the Muslim world. The head of Saudi Arabia's Shura Council, the kingdom's main government advisory body, called it an “unprecedented” incident.

'No more red lines'

“This crime, which causes goosebumps, could not have been perpetrated by someone who had an atom of belief in his heart,” top cleric Abdullah al-Sheikh said.

Cairo-based Al-Azhar, the highest authority in Islam, condemned the attacks and stressed “the sanctity of the houses of Allah, especially the Prophet's (PBUH) Mosque.”

Saudi Arabia's supreme council of clerics said the blasts “prove that those renegades... have violated everything that is sacred.” The attack drew condemnation across Islam's religious divide, with Iran calling for Muslim unity after the attacks in its regional rival.

“There are no more red lines left for terrorists to cross. Sunnis, Shias will both remain victims unless we stand united as one,” Iranian Foreign Minister Mohammad Javad Zarif said on Twitter.

Lebanon-based militant group Hezbollah — which Saudi Arabia accuses of supporting “terrorist acts” across the region — also denounced the Madinah attack as “a new sign of the terrorists' contempt for all that Muslims consider sacred.”

The governments of Turkey and Lebanon joined in the condemnation, while Iraq said the attacks amounted to “heinous crimes”.

Middle East expert Madhawi al-Rasheed said the attack in Madinah appeared aimed at humiliating the Saudi government, 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's Middle East Institute.

There also seemed to be an “organised effort by the perpetrators to coordinate their work,” potentially signalling a worsening security situation in Saudi, she said.