ISLAMABAD (Reuters) - Pakistan summoned India’s deputy high commissioner in Islamabad on Monday after four Pakistani soldiers were killed in shelling by Indian forces in the disputed Kashmir region, the Pakistani foreign office said.

The latest clash between the nuclear-armed neighbors comes amid heated challenges and threats of armed conflict.

A decades-old dispute over the mostly Muslim Himalayan region of Kashmir, claimed in full but ruled in part by both Pakistan and India, has heated up after a 2003 ceasefire brought more than a decade of relative peace.

“Despite calls for restraint, India continues to indulge in ceasefire violations. In 2018, the Indian forces have carried out more than 100 ceasefire violations,” the foreign office said, after summoning deputy high commissioner J.P. Singh.

Pakistan’s military earlier said that troops carrying out maintenance work were fired upon by Indian forces, adding that Pakistani forces responded, killing three Indian soldiers and wounding several others.

India’s military told Reuters that Pakistani forces fired first and no casualties were recorded on the Indian side.

On another section of the so-called Line of Control dividing Kashmir between the two sides, India said its forces on Monday killed five members of a pro-Pakistan militant group trying to slip into Indian Kashmir.

A Pakistani military source, who declined to be identified, denied that any militants had been killed trying to cross from the Pakistani side to the Indian side.

India accuses Pakistan of backing Islamist militants and encouraging them to launch attacks in Indian-controlled Kashmir, where a separatist insurgency has simmered for years, and in other parts of India.

Pakistan denies that and says India must hold negotiations on the future of Kashmir.

The neighbors have fought three wars since their independence from Britain, two of them over Kashmir.

Artillery exchanges across the LoC were common for years before the 2003 ceasefire in Kashmir largely brought an end to violence but clashes have been increasing over the past couple of years.

Relations have been particularly tense since India said it carried out cross-border surgical strikes against militants hiding in Pakistan in 2016. Pakistan said Indian forces never crossed onto its territory.

On Friday, Indian army chief General Bipin Rawat said his forces were willing to carry out operations inside Pakistan despite the risk of a nuclear conflict, the Indian daily the Hindustan Times reported.

The comment drew derision from Pakistan’s foreign minister who termed the statement “irresponsible” and an “invitation for nuclear encounter”.

Pakistan’s military has said 52 civilians were killed and 254 wounded by Indian shelling in the region last year, more than in all of the previous 14 years combined.