Muslim worshippers gather after a suicide bomber detonated a device near the security headquarters of the Prophet's Mosque in Medina, Saudi Arabia, July 4, 2016. [Photo/Agencies]

RIYADH - Suicide bombers struck three cities across Saudi Arabia on Monday, killing at least four security officers in an apparently coordinated campaign of attacks as Saudis prepared to break their fast on the penultimate day of the holy month of Ramadan.

The explosions targeting US diplomats, Shi'ite worshippers and a security headquarters at a mosque in the holy city of Medina followed days of mass killings claimed by the Islamic State 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 Islamic holy month.

A suicide bomber detonated a bomb at a parking lot outside the Prophet's Mosque in Medina, the second-holiest site in Islam, a Saudi security spokesman told state news agency SPA.

"Security men noticed a suspicious person among those approaching the Prophet's Mosque in an open area used as parking lots for visitors' cars. As they confronted him, he blew himself up with an explosive belt, which resulted in his death and the martyrdom of four of the security men," the spokesman said.

Five other officers were wounded, the statement added.

A Saudi security official said an attacker parked a car near the US consulate in Jeddah before detonating the device.

A video sent by a witness to the aftermath of the Medina bombing showed a large blaze among parked cars in the fading evening light, with the sound of sirens in the background. A picture showed a burnt and bleeding man lying on a stretcher in a hospital.