By Aftab Ahmed and Sarita Chaganti Singh

SRINAGAR (Reuters) - India has advanced the start date of four under-construction hydropower projects in the Kashmir region by months after suspending a water-sharing treaty with Pakistan that had slowed progress, according to an industry source and a government document.

The updated schedule for the projects, whose construction Pakistan generally opposes because it fears it would lead to less water downstream, is another sign of how India is trying to take advantage of its unilateral suspension of the Indus Waters Treaty of 1960 following a deadly attack in Kashmir last month.

India has said two of the "terrorists" who killed 26 men at a popular tourist site in Kashmir on April 22 came from Pakistan, and has taken a series of diplomatic and economic steps against Islamabad as ties between the nuclear-armed neighbours nosedive.

Islamabad has denied any role in the attack, threatened legal action over the suspension, and said any "attempt to stop or divert the flow of water belonging to Pakistan ... will be considered as an act of war". Pakistan depends on the Indus system for 80% of its farms and most of its hydroelectric output.

The armies have exchanged small arms fire across the border every night for nearly two weeks and Pakistan says India is on the verge of a military assault.

New Delhi has so far ignored Pakistan's threats and made moves that have already throttled water supplies to Pakistan, including by running maintenance work to raise the holding capacity of two operational hydroelectric plants in the federal territory of Jammu and Kashmir.

Prime Minister Narendra Modi's government has asked authorities to clear hurdles to speedy construction of four hydro projects with a combined capacity of 3,014 megawatts, according to the document, an undated list made by the power ministry and reviewed by Reuters.

The four projects are: Pakal Dul (1,000 MW), Kiru (624 MW), Kwar (540 MW) and Ratle (850 MW). All of them are on the Chenab River, whose waters are mainly meant for Pakistan but India is allowed to build run-of-water hydro projects without any significant storage.

State-run NHPC, India's biggest hydropower company, is building all the projects. They are due to start between June 2026 and August 2028, the document shows.

Various agencies, including those looking at law enforcement and labour supply, have been asked to help speed up the work, according to the document.

NHPC and the Indian ministries of power, water resources and foreign affairs did not immediately respond to requests for comment.

Pakistan's Indus River System Authority said its officials held a meeting on Monday and "noted with concern unanimously that a sudden decrease in River Chenab inflows at Marala (the headworks that regulates flow) due to short supply by India would result in more shortages" for summer crops.

Downstream reservoirs would be used pragmatically "keeping in view the crisis created by Indian short supplies in the Chenab River", the authority said in a statement late on Monday.

'PLANS FOR MORE'

India's water minister vowed last month to "ensure no drop of the Indus River's water reaches Pakistan".

The Indian industry source said there had been several meetings of officials from various private and government agencies with the power ministry in the past week about projects in Jammu and Kashmir.

"Generally, instructions to fast-track existing projects like this mean that the government wants to plan new ones," said the source, who declined to be identified since the issue was sensitive.

In total, India wants work expedited on a total of seven projects with a combined capacity of 7 gigawatts, costing about 400 billion rupees (about $4.73 billion). Reuters could not identify all the projects.

Pakistan and India are already in dispute over Ratle in the Permanent Court of Arbitration in the Hague. The dispute is about the pondage, or small water storage area, the turbine design and some other specifications.

The water treaty had required New Delhi to share with Islamabad extensive details on projects on the three Indus rivers meant for Pakistan - the Indus itself, the Chenab and the Jhelum. Modi's government has been seeking a modification of the treaty citing India's population growth and the need for more cleaner forms of energy like hydropower.

While government officials and experts on both sides had said India would not be able to stop water flows immediately, as the treaty allowed it only to build plants which do not require significant storage dams, a Pakistan official said flows from the Chenab river had already fallen drastically.

Since Sunday, the water flow has fallen by 90% from usual levels, Muhammad Khalid Idrees Rana, a spokesperson for Pakistan's Indus River System Authority, told Bloomberg News.

A source at Pakistan's Indus authority said there have been major swings in Chenab flow since Sunday, when water at the Marala headworks was 31,000 cusecs, then fell to 3,100 cusecs on Monday, and was now back up to 25,000.

"The variations in the water supply are because of India's work at (some hydro projects)," said the source. "They can do these variations where they stop water and then dump. The magnitude of these variations can't cause major damage ... but they do impact the canals."

(Reporting by Aftab Ahmed in Srinagar and Sarita Chaganti Singh in New Delhi; Additional reporting by Ariba Shahid in Karachi; Writing by Krishna N. Das; Editing by Raju Gopalakrishnan)