Dhaka, April 24 -- Tensions between India and Pakistan escalated sharply on Thursday after a deadly attack in Kashmir killed 26 people, prompting New Delhi to launch a diplomatic offensive against Islamabad and suspend a landmark water-sharing treaty that had withstood wars and border skirmishes for over six decades.

India accused Pakistan of backing the assault in Kashmir's tourist town Pahalgam, which shattered claims of calm in the disputed region and fuelled demands for a strong response from Prime Minister Narendra Modi's government.

India's Foreign Secretary Vikram Misri announced late Wednesday that several Pakistani diplomats were asked to leave the country.

In a statement issued Thursday, India's foreign ministry said all visa...