ISLAMABAD -- Britain's top diplomat on Thursday urged Pakistan and India to find a lasting solution for Kashmir a day after a deadly exchange of fire killed more than a dozen people in the disputed Himalayan region.

But after meeting with Pakistani officials, Foreign Secretary Boris Johnson told reporters in Islamabad that it was up to the two South Asian countries to resolve the crisis and that Britain should not "prescribe a solution or act as a mediator."

India meanwhile summoned a Pakistani diplomat to lodge a protest over what it said were continued violations of a 2003 cease-fire. Indian Foreign Ministry spokesman Vikas Swarup said Pakistani troops had helped "terrorists" infiltrate Kashmir, where they killed three Indian soldiers and mutilated one of their bodies, which was found Tuesday.

India had vowed to retaliate after the body was found, and on Wednesday the two sides blasted away at each other across the Line of Control, the latest in a series of violent exchanges in recent weeks. Indian fire struck a bus on the Pakistani side, killing at least 10 people. Another two Pakistani civilians and three Pakistani soldiers were also killed. There was no immediate word of Indian casualties.

The nuclear-armed rivals each claim Kashmir in its entirety and have fought two of their three wars over the dispute.

Pakistani Prime Minister Nawaz Sharif held a high-level security meeting to review the Kashmir situation on Thursday and said "we will never abandon our Kashmiri brethren in their freedom struggle," according to a government statement.

Pakistan's air force chief Sohail Aman meanwhile warned India against escalating the dispute over Kashmir into full-scale war, saying that Pakistani troops "know full well how to deal with them."

Associated Press writer Muneeza Naqvi in New Delhi contributed