Three suicide bombers struck in Saudi Arabia on Monday in a rare incidence of multiple attacks in the kingdom where the Islamic State group has previously staged deadly attacks.
There were no immediate claims of responsibility.
The latest explosion occurred at one of Islam's three holiest sites, the Prophet's Mosque in Medina in the kingdom's west, Saudi-owned Al-Arabiya news channel reported.
Other blasts occurred in the Red Sea city of Jeddah near the US consulate and in Shiite-dominated Qatif on the other side of the country.
The interior ministry said two security officers were wounded in the Jeddah bombing.
Residents of Qatif said only the bomber died in that attack, blowing his body apart near a Shia mosque.
Al-Arabiya said the Medina incident occurred during sunset prayers after which Muslims break their fast during the holy month of Ramadan, which ends Tuesday.
It showed images of fire raging in a security forces parking lot with at least one body nearby.
The Prophet's Mosque is particularly crowded during the holy month of Ramadan, which is supposed to be a time of charity but has seen spectacular attacks around the region.
Sunni extremists from IS claimed, or weer blamed for, a suicide bombing in Baghdad on Sunday that killed more than 200 people as well as other attacks in Bangladesh and at Istanbul's Ataturk airport.
At about the same time as the Medina blast, another bomber killed himself in Qatif, residents there said.
"Suicide bomber for sure. I can see the body" torn apart, said one witness to the attack in Qatif.
Nasima al-Sada, another resident, told AFP that "one bomber blew himself up near the mosque", frequented by Shiites in downtown Qatif on the Gulf coast.
No bystanders were hurt, she said.
Another witness, who gave his name only as Ayman, told AFP there were two explosions near the mosque.
"One of them was from a car parked outside the mosque and in which there was a man who was, unusually, not joining the prayer," Ayman said.
Pictures said to be from the scene and circulated by residents showed a small fire burning in the street, severed limbs and what appeared to be a severed head.