Indian Prime Minister Narendra Modi was preparing Thursday to be sworn in for a third term after an unexpectedly close election that forced his party into a coalition government.

Modi's Hindu-nationalist Bharatiya Janata Party (BJP), which had ruled for the past decade with an outright majority, had been expecting another landslide win.

But results of the six-week election released Tuesday ran counter to exit polls, seeing the BJP lose its majority and sending it into quick-fire talks to lock in an alliance that would allow it to govern.

That 15-member grouping -- the National Democratic Alliance (NDA) coalition -- announced late Wednesday that they had agreed to form a government.

"We all unanimously choose respected NDA leader Narendra Modi as our leader," a BJP-issued alliance statement said.

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

Indian media reports said Modi would be sworn in as prime minister on Saturday.

Analysts said Modi's reliance on coalition partners means he faces the prospect of a far tougher-than-expected third term.

"It will force Modi to take the point of view of others -- we shall see more democracy and a healthy parliament," said Nilanjan Mukhopadhyay, who has written a biography of Modi.

"He will have to be a leader that he has never been; we will have to see a new Modi."

- 'New chapter of development' -

While Modi faces a more complicated political environment at home, he won the plaudits of leaders from around the world.

US President Joe Biden congratulated Modi on his coalition's victory, and the State Department said the United States hoped to work with the Hindu nationalist leader on a "free and open" Asia.

"The friendship between our nations is only growing as we unlock a shared future of unlimited potential," Biden wrote on X, the former Twitter.

French President Emmanuel Macron also congratulated his "dear friend".

"Together we will continue strengthening the strategic partnership that unites India and France," Macron wrote on X.

Rival China congratulated Modi and said it was "ready to work" with its neighbour.

Russia and Japan also applauded the win, as did Britain's Rishi Sunak, his country's first Hindu prime minister, and European Union chief Charles Michel.

Modi, 73, insisted on Tuesday night 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. "This is Modi's guarantee."

Some newspapers offered a less exhilarated view.

"India cuts Modi down," The Telegraph daily, from the opposition stronghold state of West Bengal, splashed across its front page.

"Coalition Karma," read the headline of India's Mint newspaper.

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 seats short of a majority on its own.

The main opposition Congress party won 99 seats in a remarkable turnaround, almost doubling its 2019 tally of 52.

Congress party president Mallikarjun Kharge said the result was a vote against Modi "and the substance and style of his politics".

"It is a huge political loss for him personally apart from being a clear moral defeat as well," he told party leaders at an opposition alliance meeting.

In a personal sting, Modi was re-elected to his constituency representing the Hindu holy city of Varanasi with a far lower margin of 152,300 votes. That compared with nearly half a million votes five years ago.