ISLAMABAD/NEW DELHI (Reuters) - Pakistan would treat it as “an act of war” if India revoked the Indus Water Treaty regulating river flows between the two nations, Pakistan’s top foreign official said on Tuesday.

Kashmiri boatmen extract sand from the Jhelum river in Srinagar, September 26, 2016. REUTERS/Danish Ismail

Tension has been mounting between the nuclear-armed neighbours since at least 18 Indian soldiers in the disputed Kashmir region were killed this month in an attack that New Delhi blames on Pakistan.

India on Tuesday summoned Pakistan’s High Commissioner in New Delhi to inform him about two men from Pakistan now in Indian custody who it alleges helped gunmen cross the disputed Kashmir border before the attack. Pakistan denies involvement in the raid and has urged India to conduct a proper investigation.

One retaliatory move being considered by Prime Minister Narendra Modi is for India to “maximise” the amount of water it uses including by accelerating building of new hydropower plants, along three rivers that flow into Pakistan, a source with knowledge of a meeting attended by Modi on Monday told Reuters.

The source said India does not plan to abrogate the decades-old Indus Water Treaty. But using more of the rivers’ water is still likely to hurt Pakistan as the Islamic Republic depends on snow-fed Himalayan rivers for everything from drinking water to agriculture.

Sartaj Aziz, foreign policy adviser to Prime Minister Nawaz Sharif, said Islamabad would seek arbitration with the Indus Water Commission which monitors the treaty if India increased the use of water from the Chenab, Jhelum and Indus rivers.

However, if India revoked the treaty, Aziz said Pakistan would treat that as “an act of war or a hostile act against Pakistan.”

“It’s highly irresponsible on part of India to even consider revocation of the Indus Water Treaty,” Aziz told the national assembly.

The treaty was signed in 1960 in a bid to resolve disputes, but India’s ambitious irrigation plans and construction of thousands of upstream dams has continued to annoy Pakistan. India says its use of upstream water is strictly in line with the agreement.

India currently generates about 3,000 megawatts of energy from hydropower plants along rivers in its portion of Kashmir, but believes the region has the potential to produce 18,000 megawatts and says it can use more water and still remain within the terms of the treaty.

Aziz said India’s provocative posturing constitutes a breach of the Indus Water Treaty and “threats of a water war are part of a military, economic and diplomatic campaign to build pressure on Pakistan”, and deflect attention from civil unrest by the Muslim population in the Indian-ruled side of Kashmir.

DETAINED BY VILLAGERS

The attack on the Indian brigade headquarters in the Kashmir town of Uri before dawn on Sept. 18 was the deadliest in 14 years in the disputed Himalayan region and has sharply raised tensions between the arch-rivals.

India on Tuesday told Pakistan’s High Commissioner that security forces had in their custody two men - a 19-year old and a 20-year old - who helped a group of gunmen cross the de facto border dividing Kashmir before launching the Sept. 18 raid, and that they were from Pakistan-controlled Kashmir.

In a statement, India’s foreign ministry said the two men were apprehended by local villagers on Sept. 21, and that one of them had since admitted their role as guides and also identified one of the gunmen as a Pakistani from Muzaffarabad.

Reuters could not independently verify these claims.

A Pakistan foreign ministry spokesman did not immediately respond to a request for comment.