The sparring between India and Pakistan last month threatened to spiral out of control, and only interventions by U.S. officials, including national security adviser John Bolton, headed off a bigger conflict, five sources familiar with the events said.

At one stage, India threatened to fire at least six missiles at Pakistan, and Islamabad said it would respond with its own missile strikes "three times over," according to Western diplomats and government sources in New Delhi, Islamabad and Washington.

The way in which tensions suddenly worsened and threatened to trigger a war between the nuclear-armed nations shows how the Kashmir region, which both claim and is at the core of their enmity, remains one of the world's most dangerous flash points.