There was no immediate word on the fate of his two Al Jazeera colleagues - Canadian-Egyptian Mohamed Fahmy and Egyptian national Baher Mohamed - who were also jailed in the case that provoked an international outcry.

The three were sentenced to seven to 10 years on charges including spreading lies to help a "terrorist organisation" - a reference to the outlawed Muslim Brotherhood.

Greste's release came as Egypt is reeling from one of the bloodiest attacks in years. More than 30 security forces were killed on Thursday night in Sinai, and ensuing comments from President Abdel Fattah al-Sisi suggested he was in no mood for compromise.

Many Egyptians see Qatar-based Al Jazeera as a force determined to destabilise the country, a view that has been encouraged in the local media, which has labelled the journalists "The Marriott Cell" because they worked from a hotel of the U.S.-based chain.

Egyptian authorities accuse Al Jazeera of backing the Muslim Brotherhood, the movement which then army chief Sisi toppled in 2013.

The case has contributed to tensions between Egypt and Qatar, though speculation had been rising that Saudi mediation had improved ties, raising he possibility that Sisi would deport or pardon the journalists.