3 bombings occured outside Islam's second holiest site, the Prophet Muhammed's Mosque in Medina, the other near the US consulate in Jeddah & a third in the city of Qatif.
Suicide bombers struck three cities across the Kingdom of Saudi Arabia on Monday, in an apparently coordinated campaign of attacks as Saudis prepared to break their fast on the penultimate day of the holy month of Ramadan.
Only one bomber has so far been identified according to the country's Interior Ministry.
The ministry said 34-year-old Pakistani national Abdullah Qlazar Khan had blown himself up with an explosives belt.
According to the ministry, Khan had lived in Jeddah with his wife and one of her parents after coming to the kingdom 12 years ago to work as a driver.
The ministry confirmed that four security officers were killed and five others injured in the third bombing at dusk targeting Prophet Muhammed's Mosque in Medina, Islam's second holiest site.
The bombing happened as thousands of Muslims from around the world who are visiting, were about to break their fast.
The second explosion during earlier had targeted a Shia mosque in the eastern city of Qatif while the first, which happened before dawn, targeted US diplomats near the US embassy in Jeddah.
The attacks follow days of mass killings claimed by the DAESH terrorist group, in Turkey, Bangladesh and Iraq.
The attacks all seem to have been timed to coincide with the approach of Eid al Fitr, the holiday that celebrates the end of the fast.
Images on social media showed dark smoke billowing from flames near the Mosque of the Prophet, originally built in the 7th century by the Prophet Muhammad, who is buried there along with his first two successors.
The explosion in Qatif, home to kingdom's Shiite minority, struck near a mosque frequented by Shias.
Witnesses described body parts, apparently of the bomber, in the aftermath.
A Saudi security official said Khan had parked a car near the US consulate in Jeddah before detonating his explosives belt.
The Jeddah blast was the first bombing in years to attempt to target foreigners in the kingdom.
There was no immediate claim of responsibility, but officials say evidence points towards the DAESH terrorist group.
DAESH has carried out a series of bombing and shooting attacks in Saudi Arabia since mid-2014 that have killed scores of people, mostly members of the Shiite Muslim minority and security services.
Police and groups of local volunteers increased security near mosques in Qatif after suicide bombings hit mosques in Shiite areas last year, killing dozens.
Another suicide blast at a mosque used by security forces also killed 15 a year ago.