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 had been expected to bring a swift end to weeks of escalating clashes triggered by the mass shooting of tourists last month that India blames on Pakistan.

The Indian military sent a “hotline message” to Pakistan on Sunday about violations of a ceasefire agreed this week and informed it of New Delhi’s intent to respond if it was repeated, a top Indian army officer said, while the Pakistan military’s spokesman denied any violation of the ceasefire.