India and Pakistan have blamed one another for cross-border shelling in the disputed Kashmir region that has killed and injured soldiers and civilians on both sides and made it one of the deadliest days since Delhi revoked Kashmir’s special status in August.

India said there was heavy shelling by Pakistan across the border in the Tangdhar region of northern Kashmir on Saturday night, killing two Indian soldiers and one civilian. Islamabad said one of its soldiers and three civilians died after India violated the ceasefire, according to a spokesman for the Pakistani armed forces.

Kashmir has been a disputed territory for the nuclear-armed neighbours since they both gained independence in 1947, and they have fought two of their three wars over the region.

Tensions between the countries have flared and there has been intermittent cross-border firing since 5 August, when Delhi flooded Indian Kashmir with troops to quell unrest after it revoked the region’s special autonomous status.

Islamabad has warned that changing Kashmir’s status would escalate tensions, but India says it is an internal affair and is aimed at faster economic development of the territory.

The shelling marks an escalation from the small-arms fire usually exchanged by the two armies.

There was an unprovoked ceasefire violation by Pakistan, said Indian defence spokesman Col Rajesh Kalia. “Our troops retaliated strongly, causing heavy damage and casualties to the enemy,” he added.

An Indian army source said the shelling was cover to help Pakistani militants enter India, because of which a “calibrated escalation of area weapons was undertaken”. The Indian army “retains the right to respond at a time and place of its choosing” if the Pakistani army continued to do this, he said.

Pakistan, meanwhile, claimed India’s attack was unprovoked and deliberately targeted civilians.

Maj Gen Asif Ghafoor, a spokesman for the Pakistan armed forces, said they responded “effectively”, killing nine Indian soldiers, injuring several others and destroying two bunkers. “The Indian army shall always get a befitting response,” he said.

Raja Farooq Haider Khan, the prime minister of Pakistan’s Azad Kashmir region, said Indian forces in Kashmir had gone “berserk”, adding that six civilians died and eight were injured. “This is the height of savagery. The world must not stay silent over it. #KashmirNeedsAttention,” he said in a tweet.