Egyptian protesters have demanded the release of human rights lawyer Ahmed al-Gizawi.
He was detained earlier this month on arrival in Saudi Arabia and accused of insulting King Abdullah.
Egyptian activists say the lawyer was held after lodging a complaint against Saudi Arabia for its treatment of Egyptians in its prisons.
His family say he had gone to perform a minor pilgrimage - a detail which has angered many Egyptians who feel resentment at the kingdom's treatment of Egyptians.
But Saudi authorities say Mr al-Gizawi was found by airport officials to be carrying drugs - allegedly more than 20,000 anti-anxiety pills - in his luggage.
They say they doubt Mr al-Gizawi was on a pilgrimage, as he was not wearing white pilgrims' clothes.