Indian Prime Minister Narendra Modi is expected to present a coalition agreement to the president on Friday, after an unexpectedly close election forced his party to rely on allies to keep him in power.

Modi's Hindu-nationalist Bharatiya Janata Party (BJP) ruled outright for the past decade but failed to repeat its prior two landslide wins, defying analyst expectations and exit polls.

It was instead forced into quick-fire talks with a 15-member coalition that agreed to give it the parliamentary numbers to govern.

Modi was expected to visit President Droupadi Murmu with allied party leaders on Friday to seek her formal approval to form the next government, news agency Press Trust of India reported.

The National Democratic Alliance (NDA) supporting Modi's third term ambitions "unanimously" chose the 73-year-old premier as leader on Wednesday.

The alliance holds 293 seats in parliament, giving it control of the 543-seat body.

Modi's party has not revealed what concessions alliance members were given to secure their support, but several larger parties were seeking plum ministerial portfolios.

The Indian Express reported Friday that the Telugu Desam Party (TDP) from the southern state of Andhra Pradesh -- the largest BJP ally with 16 seats -- would press for the revival of plans to build a new state legislative capital.

The BJP's second-biggest ally, the Janata Dal (United) party of Bihar state, was meanwhile seeking a review of a contentious army recruitment scheme introduced by the government in 2022 to cut military expenditure.

Modi's new reliance on "the minefield of coalition politics" meant he faced the prospect of a far tougher-than-expected third term, the Hindustan Times warned in its Thursday editorial.

Indian media reports said Modi was likely to be sworn in as prime minister on Sunday.

Regional leaders including Sheikh Hasina of Bangladesh and Sri Lankan President Ranil Wickremesinghe have said they will attend the ceremony.

Modi insisted on Tuesday that the election results were a victory that ensured he would continue his agenda.

"Our third term will be one of big decisions and the country will write a new chapter of development," Modi told a crowd of cheering supporters in the capital New Delhi after his win.

Commentators and exit polls had projected an overwhelming victory for Modi, who critics have accused of leading the jailing of opposition figures and trampling on the rights of India's 200-million-plus Muslim community.

But the BJP secured 240 seats in parliament, well down from the 303 it won five years ago and 32 short of a majority on its own.