Islamic State has threatened to destroy Saudi Arabian prisons holding jihadists after Riyadh's execution of 47 people including 43 convicted al Qaeda militants.
The militant group, which has claimed responsibility for attacks in the kingdom and stepped up operations in neighbouring Yemen, singled out the al-Ha'ir and Tarfiya prisons where many al Qaeda and Islamic State supporters have been detained.
"The Islamic State always seeks to free prisoners, but we calculate that the ending of the issues of prisoners will not happen except with the eradication of the rule of tyrants, and then destroying their prisons and razing them to the ground," it said in an article posted online on Tuesday.
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An Islamic State supporter killed himself in a car bomb at a checkpoint outside Ha'ir prison near Riyadh in July.
While Islamic State and al Qaeda are rivals who have condemned each other on ideological grounds, they are both united in enmity towards Saudi Arabia, which has declared them terrorist groups and locked up thousands of their supporters.
Riyadh's mass execution on Saturday included four Shi'ite Muslims, among them prominent cleric Nimr al-Nimr, a move that heightened sectarian tensions with Shi'ite power Iran. But analysts say it was mostly meant as a message to militant Sunnis.
Islamic State has claimed responsibility for a series of bombings and shootings in Saudi Arabia since November 2014 that have killed more than 50 people, most of them Shi'ites but also more than 15 members of the security forces.
Saudi security officials say the group's supporters inside Saudi Arabia mainly act independently, depending on Islamic State for only limited logistical help and advice, making them harder to detect, but also less capable of attacks on well protected targets.
Al Qaeda in the Arabian Pensinula (AQAP) threatened in December to "shed the blood of the soldiers of Al Saud" if its members were executed.
AQAP is the Yemen-based wing of the global militant movement and was formed by local jihadists and veterans of al Qaeda's earlier uprising in Saudi Arabia from 2003-06, for participation in which most of those executed on Saturday were convicted.
