Sheila Tiwari, the executive editor of the Indian Express, was among those who had been in touch with his wife.

She said she was “very sad to hear about her passing”, adding that people of all walks of life would be “thrilled” to hear his views on the present environment and what was needed to address it.

In a column in The Hindu earlier this week, Mr Modi claimed that India had not taken the wrong path by seeking its own foreign policy at the expense of the US.

The US has, however, accused India of “sedition and subversion” in the past for advocating hardliner foreign policy.

In its report, The Indian Express also described the family’s life as “exemplary”, describing Mr Rajan and Miss Tiwari’s “warm friendship”.

Sushma Swaraj was quoted as saying that their daughter and son-in-law had both been educated in private colleges and would be “truly missed” by everyone.

A number of prominent politicians condemned the assassination, including former chief ministers of Maharashtra, Madhya Pradesh and Gujarat and the leader of the ruling AIADMK party, M. Veerappa Moily.

The Maharashtra government called on “all political parties to condemn this cowardly act” while Rajasthan governor G.K.Ohedkar condemned “in the strongest terms” the “despicable murder” in a statement.

The Opposition Congress said Mr Modi’s Bharatiya Janata Party (BJP) government deserved “greater condemnation” for “a brazen act”.

Mr Modi has been criticised for his policies including his push to make an India of Muslims, which they say amounts to religious cleansing, and his promise to end “caste-based reservation”.

His government has been criticised for the land acquisition Bill being opposed by the ruling Congress party.

However, both its president Sonia Gandhi and vice-president Rahul Gandhi have stood by Mr Modi’s policies in the face of criticism.

In another development, Mr Modi was reported to be travelling to London to participate in the Commonwealth Heads of Government Meeting in August, an event which was cancelled in the run up to Mr Rajan’s appointment.

Mr Modi was also reported to have called on his supporters abroad, calling on them to follow India’s example by voting.

The BJP had planned to hold a huge rally on