Indian villagers board a bus provided by the government as they leave one of the areas allegedly shelled from the Pakistani side of the disputed Kashmir border. (Jaipal Singh/European Pressphoto Agency)

Leaders in India and Pakistan traded blame Thursday for cross-border attacks that officials said have killed at least 18 civilians in recent days and forced thousands from their homes.

Villagers in the disputed Kashmir region have fled an unusually intense spate of mortar shelling that has gone on for more than a week along the border, one of the most highly militarized zones in the world. It is some of the worst violence between the nuclear-armed neighbors since a 2003 cease-fire.

India’s defense minister, Arun Jaitley, called on Pakistan to stop “unprovoked” attacks and issued a warning.

“If Pakistan persists with this adventurism, then our forces will continue to fight,” Jaitley said at a news conference in New Delhi. “The cost of this adventurism will be unaffordable.”

In Pakistan, a military spokesman said 10 Pakistani civilians had been killed and more than 42 injured during the shelling.

Indian villagers sit on bus provided by the government as they leave one of the areas allegedly shelled from the Pakistani side of the disputed Kashmir border. (Jaipal Singh/EPA)

“During the last three days, Indian troops are repeatedly resorting to unprovoked firing,” the spokesman said. Pakistani troops are meeting the fire with “an effective response,” he added.

The United Nations has expressed concern about “the recent escalation of violence.” The U.N. secretary general wants both nations “to engage constructively to find a long-term solution for peace and stability in Kashmir,” his spokesman said in a statement Thursday.

Rajesh Kumar, the inspector general of police in the Jammu region, on the Indian side, said that border clashes have been common over the years but that the intensity of the shelling this time was “very high” compared with past incidents, with shelling occurring even during daylight hours. He said eight Indian civilians had been killed in the latest shelling.

The two countries have struggled over their disputed border and the territory of Kashmir — including in two wars — since Muslim-majority Pakistan was carved out of Hindu-dominated India in 1947.

The escalating border crisis is the first between the countries since Indian Prime Minister Narendra Modi, a Hindu nationalist, took office in May. Modi had made a point to invite Pakistani Prime Minister Nawaz Sharif to his swearing-in, but the goodwill faded when border clashes erupted in the summer.

Modi was asked about the issue while attending a military ceremony Wednesday and replied tersely: “Everything will be fine soon.”

Although Sharif plans to convene his National Security Council on Friday to discuss the fighting, there was no sign of urgency or concern within the government, officials in Pakistan said.

Instead, Sharif traveled Thursday to Pakistan’s North Waziristan tribal region to meet with soldiers engaged in a four-month-old operation against the Taliban in the area.

Kumar, the police official, estimated that 50,000 villagers in India have been affected by the ongoing conflict and that many were living in temporary camps. Thousands in the region were already displaced by severe flooding last month.

“We have never seen such shelling on the border,” said Shanti Lal, 53, a villager from Trewa. “There were bombs and rockets flying all over our village.”

Lal said the villagers stayed in their homes for the first two days of attacks, then escaped, leaving behind everything they owned. About 400 from his village are living with relatives or in temporary camps, he said, and the uncertainty is devastating.

“We don’t know when it’s going to end,” Lal said. “Our cattle would be starving by now, and we have no clue about our house.”

Tim Craig and Shaiq Hussein in Islamabad, Pakistan, and Jalees Andrabi in New Delhi contributed to this report.