RIYADH, July 4 (Reuters) - A suicide bomber detonated a device near the security headquarters of the Prophet's Mosque in Medina, Saudi Arabia, the second-holiest site in Islam, Saudi-owned al-Arabiya television reported on Monday.

The blast followed others in Qatif and Jeddah on Monday, the last day of the Muslim holy fasting month of Ramadan and start of the Eid al-Fitra festival. Pictures circulating on social media showed dark smoke billowing from flames near the mosque.

(Reporting By Ali Abdellati in Cairo; Writing by Angus McDowall, editing by Larry King.) ((angus.mcdowall@thomsonreuters.com; Reuters Messaging: angus.mcdowall.thomsonreuters.com@reuters.net))