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 truce came after several days of the countries’ most expansive fighting in decades. One Indian official said the country would “deal strongly” with any violations.

ISLAMABAD — Pakistan armed forces said they are targeting military sites in India after India fired missiles at three air bases in Pakistan’s Punjab province early Saturday, bringing the nuclear-armed rivals closer to war.