India committed in 1999 to not being the first to use nuclear weapons in any conflict. Among India's neighbours China has a similar doctrine but arch rival Pakistan does not.

Defence Minister Rajnath Singh made the comment on Twitter after visiting Pokhran, the site of India's successful nuclear tests in 1998 under then prime minister Atal Vajpayee.

"Pokhran is the area which witnessed (Vajpayee's) firm resolve to make India a nuclear power and yet remain firmly committed to the doctrine of 'No First Use'," Singh wrote.

"India has strictly adhered to this doctrine. What happens in future depends on the circumstances," Singh tweeted.

The statement comes as tensions rise with Pakistan after Prime Minister Narendra Modi's government stripped Indian-administered Kashmir of its autonomy, a move sharply condemned by Islamabad.

- 'Stop lying' -

Singh's comments prompted considerable noise in both India and Pakistan, with Pakistan's minister for human rights Shireen Mazari tweeting that India "need to stop lying".

"India's claims to NFU ended when on 4 Jan 2003 Indian govt declared it would use nuclear weapons against any (even Chemical or Biological) attack 'against India or Indian forces anywhere'," she said.

Observers said Singh's statement is the clearest so far with regards to a change in India's nuclear doctrine.

Vipin Narang, a professor at the Massachusetts Institute of Technology, tweeted it was the "highest level declaration that India may not feel indefinitely or absolutely bound to No First Use."

Singh received support from Subramanian Swamy, a hardliner parliamentarian from Modi's Bharatiya Janata Party (BJP).

"Rajnath is correct as to warn about possible review of Vajpayee's no first use of n weapons since Pak leadership is more crazed today than in 1998," he tweeted.

"First use is required now on if we get credible evidence that Pak faced with ignominy may go for first strike. We must pre-empt that," Swamy wrote.

This is not the first time that the Modi government has made a statement regarding its nuclear policy.

In 2016, then defence minister Manohar Parrikar had expressed his reservations over the "no first use" nuclear policy.

Parrikar, who died last year, had said India was a responsible nuclear power and "it would not use it irresponsibly."

A revision to the policy was part of the BJP's election manifesto in 2014. Then front runner Modi, however, stated that if voted to power, he had no intention of changing the stance.

Running for a second term earlier this year, Modi had said his government had called Pakistan's "nuclear bluff".

"India has stopped getting scared of Pakistan's threats. Every other day they say, 'we have a nuclear button.' What do we have then? Have they kept it for Diwali?"," he said, referring to a Hindu festival when fireworks are set off.