RIYADH (AFP) - Saudi Arabia blamed the Islamic State in Iraq and Syria (ISIS) group Friday for the killing of two policemen in the capital this month and said three bomb-laden cars had been seized during its investigations.

A Saudi man arrested on suspicion of carrying out the shooting has confessed that he was following orders received from ISIS in Syria, the interior ministry said.

He was identified as 23-year-old Yazid bin Mohammed Abdulrahman Abu Niyan.

The authorities offered a one million riyal (S$355,606) bounty for a second suspect, a Saudi named as Nawaf bin Sharif Samir al-Anzi.

During their investigation the authorities seized seven cars, "three of them booby-trapped", as well as suspected bomb-making materials and tools, said the statement carried by the Saudi Press Agency.

They also discovered machine guns, ammunition, money and several mobile telephones which revealed an exchange between the attackers and "terrorist elements in Syria," it said.

The two Saudi policemen were killed in an April 8 drive-by shooting in an eastern district of Riyadh.

The ministry said that Abu Niyan had allegedly carried out the shooting while his partner, Anzi, drove the car and filmed the attack.

According to Anzi, ISIS supplied them with the weapons, ammunition, and money to carry out the shooting through a "third party whom they did not meet", the statement said.

The Sunni-dominated kingdom is part of a US-led coalition taking part in an air war against ISIS, which has seized swathes of Syria and Iraq.

Westerners have been attacked in Saudi Arabia four times since October, including in a drive-by shooting that wounded a Danish national in Riyadh on November 22.

Authorities later arrested three suspected ISIS supporters.