The Saudi interior ministry said a bombing near the U.S. consulate in Jeddah was carried out by Pakistani national Abdullah GulzarKhan, 34, a private driver who had been living with his wife and her parents in the city for 12 years.
However, Islamic State terrorist group has claimed responsibility for a string of bombings targeting minority Shia community and security forces over the past 18 months.
Saudi authorities arrested terrorism suspects in Medina in early June, but this is believed to be the first bomb attack on the city. He said nitroglycerine from the blasts in Qatif and Medina seemed to match those found at the Jeddah attack, suggesting they may have been coordinated.
The attackers in the kingdom's eastern Qatif province were named as three Saudi men, two of them 20 years old and one 23 years of age. According to reports, 12 of those arrested were Pakistani, with some of the nationalities of other attackers remaining unclear. "As they tried to stop him, he blew himself up with an explosive belt causing his death and the death of four security personnel", an official statement said, adding five others were injured.
Zeid Ra'ad Al-Hussein, the UN High Commissioner for Human Rights and a member of the Jordanian royal family, delivered his remarks via a spokesman in Geneva.
King Salman, in a speech on July 5, marking Eid al-Fitr, the holiday that celebrates the end of the Islamic holy month of Ramzan, said a major challenge facing Saudi Arabia was preserving hope for youth who faced the risk of radicalisation.
Militant attacks on Medina are unprecedented. "Sunni, Shiites will both remain victims unless we stand united as one", said Iranian Foreign Minister Javad Zarif.
"The Kingdom of Saudi Arabia is determined, God willing, to strike with an iron fist those who target the minds and attitudes of our youth", he said.
Saudi Arabia, which saw an unprecedented three suicide bombings within 24 hours on Monday, is a partner in the US-led coalition fighting Isil in Syria and Iraq.