Modi faces revived opposition

• Rahul Gandhi to rally more regional groups to rally against Modi

• Mamata Banerjee hails "victory of the regional front"

Indian opposition parties have joined forces to snatch power from the country's ruling party in a big southern state, laying the stage for other such alliances in a direct challenge to Prime Minister Narendra Modi's re-election bid next year.

A coalition of Congress and a regional group said on Sunday they will establish a government in Karnataka state next week, after Modi's Bharatiya Janata Party (BJP) failed to prove its majority despite bagging more seats than any other party in a closely-fought election.

Rahul Gandhi, the leader of the Congress party - which has struggled to make any major political inroads since Modi stormed to power four years ago - said his party will rally regional groups into a common front against Modi.

"I am very proud that the opposition has stood together and defeated the BJP, and we will continue to do so," said Gandhi.

Karnataka, with a population of 66 million, was the first major state this year to elect an assembly, and will be followed by three more before the general election in 2019.

Political strategists say polls in Karnataka were seen as a key test of Modi's popularity but the final outcome highlights the threats he faces from a united opposition are much bigger than anticipated.

Karnataka's state's governor last week allowed BJP-led alliance (104 seats) to form a government despite trailing the opposition alliance (115 seats).  Facing a trust vote, ordered by Indian top court, BJP's newly appointed state chief minister, BS Yeddyurappa, resigned.

To bring the regional party - Janata Dal (Secular) - into the alliance, Congress, which has 78 of the seats, did have to concede the chief minister's job to the smaller group. Previously, the state had been held by Congress.

Mamata Banerjee, a powerful politician in eastern India, described Modi's failure in Karnataka as a "victory of the regional front".

Modi remains by far the most popular politician in India and his approval rankings far outweigh Gandhi, who is the fifth-generation scion of the Nehru-Gandhi dynasty.

US-based research agency Pew released a survey in November that showed nearly nine out of 10 Indians held a favourable opinion of Modi.

Yesterday, Indian newspapers carried front-page headlines highlighting Modi's loss, a rare sight of late in Indian politics: The BJP and its allies rule 21 of India's 29 states currently, up from seven they ruled in 2014.

"BJP loses vote of overconfidence," said the Indian Express newspaper's front page headline.