That's according to a White House statement on a phone conversation Tuesday between the two leaders.

The White House emphasis on a full spectrum of responses underscored the potential for a military response from the U.S. and its NATO allies as Libya slips from Moammar Gadhafi's grip and into civil war.

The White House said Obama and Cameron agreed that the objective must be an end to violence and the departure of Gadhafi "as quickly as possible."

Enforcing a no-fly zone would be difficult but there have been calls for one as forces loyal to Gadhafi hammer rebels with airstrikes.