Saudi authorities said on Sunday in the Saudi capital that the four were detained as part of the investigation into last Monday's bombings that killed 34 people, including eight Americans.
Meanwhile, a senior Saudi official is defending his country's anti-terrorist efforts, while also vowing to do more to fight extremism in the aftermath of the Riyadh attacks.
Saudi Foreign Policy Advisor Adel al-Jubeir told Fox television that Saudi Arabia has tried its best to cut off funding to terrorist organizations and to find and punish terrorists.
However, Mr. al-Jubeir admitted the bombings in Riyadh showed these steps were not enough,and that Saudi Arabia must do more. He told N-B-C that he is almost certain the al-Qaida terrorist network was behind the attacks.
The Washington Post says U-S officials suspect a top al-Qaida leader believed to be hiding in Iran -- Saif Adel -- helped organize the bombings.
The newspaper says Saif Adel allegedly issued orders for the bombings to a Saudi citizen, Khaled Jehani, who Saudi and U-S officials believe was in charge of carrying out the attacks.