Police in the disputed state of Kashmir believe separatist groups are behind a spate of bank robberies across the region in the past 40 days, a new tactic indicating the militants’ finances could have been badly hit by the government’s demonetisation drive.

Three men armed with Kalashnikov rifles were involved in a robbery at a bank in Kashmir’s Pulwama district last Thursday, making off with nearly 1m rupees (£12,000) from the safe.

It was the fourth bank robbery in the region in the past three months, and the third since early November, when the Indian government announced the sudden scrapping of 1,000 and 500 rupee notes.

Police said they used CCTV in the bank to identify the robbers as Arif Dar, a local fighter, and Abu Ali and Abu Ismail, two foreigners with suspected links to to the Pakistan-based militant group Lashkar-e-Taiba.

Mohammad Rayeed Bhat, the police chief of Pulwama, said militant groups were believed to be behind all four of the robberies in recent months, linking the three most recent to the demonetisation announcement.

“It is a simple calculation,” he said, citing intelligence assessments. “Right now, militants are facing a huge cash crunch.”

Two other police officials, speaking on condition of anonymity, also told the Guardian they believed the bank heists were linked to the demonetisation policy.

The Indian economy has been operating with 60% less currency since the November announcement by the prime minister, Narendra Modi, that the country’s two most used cash bills would cease to be valid within hours.

Modi cited the need to deprive militant groups of their “black money” hoards as one of the justifications for the policy, which has been poorly implemented, suffocating the informal sector and forcing millions of Indians to stand in bank queues for hours to exchange their old currency.

The robberies in the past weeks are the first in recent years to be linked to militant groups in Kashmir, suggesting demonetisation may be impacting the separatists’ finances and forcing them to try new tactics to raise funds.

However, the two main militant groups in the region have distanced themselves from the accusations.

“Our fighters will starve but never commit such acts,” a Lashkar-e-Taiba spokesman was quoted in a statement released to local media. Hizbul Mujahideen said the robberies were the work of “anti-Islamic and anti-freedom elements”.

The past six months have been the bloodiest in the disputed region in five years, with more than 80 civilians killed in fiery protests that brought Kashmir to a halt throughout the summer.

An attack by militants at an Indian army base in Uri, near the “line of control” that separates Indian-controlled Kashmir from territory held by Pakistan, killed 19 soldiers and raised tensions between the nuclear neighbours to their highest levels since 2001.

Sixty Indian soldiers have died in the state so far this year, nearly double the number killed in 2015 and 2014.