A suicide bomber blew himself up Monday night near the Prophet's Mosque in Medina, one of Islam's holiest sites, in the third such attack of the day in Saudi Arabia.
Saudi news site Sabq, which is seen as close to the authorities in the kingdom, said the attacker targeted security officials as they ate the Iftar meal, which breaks the Ramadan fast.
Saudi-owned Al Arabiya television said four security men were killed in the blast, which set off a fire in an adjoining car park. The reported casualties could not be confirmed.
Al-Arabiya said that worshippers arrived in the mosque as usual for evening prayers after the attack. The channel broadcast what it said was video of worshippers filling a hall inside the mosque.
Also Monday evening, a double suicide attack targeted a mosque in the mainly Shiite eastern city of Qatif, Sabq reported.
The attackers in Qatif blew themselves up after failing to gain entry to the Faraj al-Omran mosque, Sabq reported. The report said unidentified body parts were found at the scene.
It was not clear whether there were any casualties other than the attackers.
The attacks came after a suicide bomber blew himself up early Monday near the US consulate in the western city of Jeddah, according to Sabq.
The Interior Ministry said that two security officers suffered minor injuries in that attack.
The wave of suicide bombings comes two days before the Eid al-Fitr feast, which marks the end of the holy month of Ramadan, during which Muslims fast daily from dawn to dusk.
There were no immediate claims of responsibility for the attacks.
The Islamic State Sunni extremist organization, which views Shiites as heretics, has claimed previous attacks in Qatif, including a May 2015 bombing attack that killed 22 worshippers at a mosque.