At least three people were killed in a blast outside the Prophet's Mosque in Medina in Saudi Arabia on Monday, including a suicide bomber and two security officers, Saudi-owned al-Arabiya television reported.
The bomber detonated his device as the security officers were breaking their day-long fast for Ramadan, Arabiya reported.
Reports of a second explosion could not be confirmed.
Photos and video showed cars on fire and smoke rising above the city. The BBC reported that the explosion occurred near the Prophet's Mosque, one of Islam's holiest sites and the burial place of the Prophet Muhammad.
Saudi Arabia has seen two other suicide attacks in the past 24 hours, with one bomber targeting the US consulate in Jeddah and another attacking a Shiite mosque in Qatif. The attacks did not result in any deaths expect for the bombers.
The attacks follow 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 fast.
A Saudi security official said an attacker parked a car near the US consulate in Jeddah before detonating the device.
In the Qatif, an eastern city that is home to many members of the Shiite minority, at least one and possibly two explosions struck near a Shi'ite mosque.
Witnesses described body parts, apparently of a suicide bomber, in the aftermath.
A resident of the city reached by telephone said there were believed to be no casualties there apart from the attacker, as worshippers had already gone home to break their fasts. Civil defence forces were cleaning up the area and police were investigating, the resident said.
A video circulating on social media and purporting to show the aftermath of a Qatif blast showed an agitated crowd on a street, with a fire raging near a building, and a bloody body part lying on the ground. Reuters could not immediately verify the video.
Hours earlier a suicide bomber was killed and two people were wounded in the blast near the US consulate in the kingdom's second city Jeddah.
The Jeddah blast was the first bombing in years to attempt to target foreigners in the kingdom. There was no immediate claim of responsibility.
Islamic State 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 people a year ago.
Image via Twitter.
Reuters contributed to this report.