The deadly violence marks the latest escalation in the Himalayan region of Kashmir, which is divided between the two nuclear-armed neighbors and claimed by both in its entirety.

According to Deputy Commissioner Waheed Khan, an artillery shell hit a passenger bus in the scenic Neelum Valley in the Pakistani part of Kashmir, killing nine people — three died on the scene and six later, at a hospital. Several people were also reported wounded in that attack.

Another two civilians died when a mortar shell hit their house in the Nakyal sector in Kotli district, said police official Waseem Khan. The shelling sent residents fleeing in panic, he said.

An army statement said Pakistani troops were firing back on Indian military positions. The statement also said that an ambulance that had rushed the scene of the attack was fired upon by India.

An Indian army spokesman, Colonel Nitin Joshi, said India was responding to Pakistan's violation of a cease-fire, adding that Pakistani troops have fired at several Indian army positions.

Another senior Indian army officer, speaking on condition of anonymity under military regulations, said that Indian troops were responding to an attack on an army patrol that killed three Indian soldiers on Tuesday.

The body of one Indian soldier was reported mutilated by the attackers and emotions have been running high following that assault.

Deadly exchanges of fire in the disputed Kashmir have intensified in recent weeks. Tensions have escalated since militants attacked an Indian army base in Kashmir in September. India said the militants were supported by Pakistan, charges denied by Islamabad.

Both sides accuse the other of initiating the firing along the Line of Control, which separates the Pakistan- and India-controlled parts of Kashmir.

So far this week, at least 18 people, civilians and soldiers, have been killed on both sides.

Last week, Pakistani army claimed to have shot down a small Indian drone in Kashmir, a day after the Pakistani navy claimed it had intercepted Indian submarines entering the country's territorial waters in the Arabian Sea.

Two of the three wars between India and Pakistan since 1947 have been fought over their competing claims to Kashmir.