We "mourn the loss of life and condemn this violence," said White House spokesman Josh Earnest. "All of the victims were Muslims. That is unfortunately all too common."
The Sunni jihadist Islamic State group has said it carried out the attack at a mosque in Saudi Arabia's predominantly Shiite Eastern Province, killing and wounding several people.
The White House said it was not ready to confirm whether that claim was legitimate.
"The attribution -- the determination about who is responsible -- is something that is still under review," said Earnest.