Cameron -- who canceled a planned Friday speech in the Netherlands -- talked Thursday with U.S. President Barack Obama about the situation, according to a Downing Street statement.
Before Algeria launched its military operation, U.S. officials had urged the Algerians to be cautious and make the hostages' safety their first priority, an Obama administration official said.
Algerian government officials did not warn their U.S. counterparts about the raid, the official said.
A senior U.S. official said U.S. officials did not trust the information they were getting from the Algerians, "because we hear one thing and then we hear something else."
Though there was concern that the Algerians' tactics may have put hostages in jeopardy, the official acknowledged they could have hit even harder.
"In all fairness, they could have ended it today," the senior U.S. official said. "They haven't used all the severeness they could. They know hostages are left."