In an attack claimed by the Islamic State jihadist group, a suicide bomber wounded two policemen at a checkpoint near a high-security prison in the Saudi capital Riyadh.
The group said that the bomber, identified by Saudi authorities as Abdullah al-Rashid, 19, had also killed his uncle, a colonel in the interior ministry, before blowing himself up, the SITE Intelligence monitoring group said.
IS's branch in Najd, the central region of Saudi Arabia, said on its Twitter account that Thursday's attack was a message to jihadists held in Riyadh's Al-Hair prison that they had not been forgotten.
"Let the Muslim captives in Al-Hair and everywhere know that we will not relent or tire until we release them from imprisonment, with permission from Allah," SITE quoted the tweet as saying.
IS named the slain colonel as Rashid Ibrahim al-Sufyan and said that Rashid had machine-gunned him in his own home.
The wounded policemen were in a "stable condition" in hospital, the interior ministry said in a statement carried by the official Saudi Press Agency.
The jihadist group, which controls swathes of Iraq and Syria, has expanded its operations into Saudi Arabia and neighbouring Kuwait and Yemen this year with a string of deadly attacks.
Most have targeted the Gulf states' Shiite communities, regarded as heretics by the Sunni extremists.