Singh posted a tweet from Pokhran, the test site of India's nuclear weapons, after paying homage to former Prime Minister Atal Bihari Vajpayee on his first death anniversary.
"Pokhran is the area which witnessed Atalji's firm resolve to make India a nuclear power and yet remain firmly committed to the doctrine of 'No First Use'. India has strictly adhered to this doctrine. What happens in future depends on the circumstances," Singh tweeted.
BJP Rajya Sabha leader Subramanian Swamy tweeted in response to Singh's statement saying he is correct in warning about a possible review of Vajpayee's no first use of nuclear weapons.
"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. First use is required now if we get credible evidence that Pak faced with ignominy may go for first strike. We must pre-empt that," tweeted Swamy.
Singh's comments come amid belligerent statements by Pakistan on Jammu and Kashmir and ahead of a 'closed door' meeting at the UN on the issue of the abrogation of special status to the state.
Singh had travelled to Pokhran after attending the closing ceremony of the International Scout Masters Competition that concluded in Jaisalmer on Friday.
The Congress has meanwhile backed Singh on the issue of 'No First Use' and declared it would endorse the policy of the BJP-led NDA government on it.
"I can assure you whatever is the policy we will welcome it and stand by it," said senior Congress leader Abhishek Manu Singhvi.
However, Singhvi also termed the statement as ambiguous and asked if Rajnath wanted to keep the country guessing over it or announce a new nuclear policy.
"Then the country will be happy to know what the new policy is, not in ambiguous and not in half phrase frame but in a full one-paragraph detailed policy," he said.
A 'No First Use' refers to a doctrine by any nuclear-powered state of not resorting to the use of atomic weapons unless it is itself first subjected to a nuclear attack by an enemy.
This is not the first instance that the NDA government has referred to a rethink about India's 'No First Use' doctrine. Former Defence Minister in the first Modi government the late Manohar Parrikar had also raised questions in November 2016 as to why should India bind itself to such a policy.
Parrikar had later clarified that the statement was his personal opinion.
( With inputs from IANS )