India and Pakistan agreed to an immediate ceasefire on Saturday, unexpectedly halting the worst fighting in decades between the nuclear-armed neighbors, just when their tit-for-tat strikes appeared to be spiraling out of control.

The ceasefire follows weeks of clashes that were triggered by a gun massacre on tourists last month that India blames on Pakistan. The first word on the truce came from U.S.

The sudden announcement of a U.S.-brokered ceasefire followed four days of steady escalation between India and Pakistan and mixed signals from Washington.