Saudi state television says King Abdullah has died at the age of 90.
His expected successor is his 79-year-old half-brother, Prince Salman, who recently has taken on the ailing king's responsibilities.
The announcement came in statement read by a presenter on Saudi state TV, which aired video of worshippers at the Kaaba in Mecca.
King Abdullah was a powerful United States ally who joined Washington's fight against al Qaida and sought to modernise the ultraconservative Muslim kingdom.
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