Preliminary results showed that the Bharatiya Janata Party (BJP) had made a strong showing in the four heartland states being contested in the Sunday poll, while the ruling Congress party suffered a loss in support.

Congress - led by the Nehru-Gandhi political dynasty - appeared set for a bruising defeat in three states - Delhi, Madhya Pradesh and Rajasthan. In the state of Chhattisgarh, Congress and the BJP were running neck and neck.

"The results in Delhi, Madhya Pradesh and Rajasthan are disappointing.... Congress accepts its defeat with great humility.... We concede that we have lost there," said party spokesman Randeep Singh Surjewala.

The ruling party, currently heading towards the end of its second term in power, has faced mounting voter dissatisfaction amid slow growth, inflation and allegations of corruption.

The vote represents the last big test ahead of a general election that is due to take place by May next year. Congress played down the defeat, but said it would aim to learn lessons.

"We accept the verdict of the people and we will introspect," said Environment Minister Jayanthi Natarajan, a member of the Congress party. "This is by no means the full picture for the general elections."

The BJP's Narendri Modi, likely to be the opposition's candidate for the premiership next year, congratulated the party's leaders in Madhya Pradesh and Rajasthan, where the BJP enjoyed a landslide.

Leading Congress figure unseated

Modi, who is likely to face Congress's Rahul Gandhi in the general election, voiced delight on Twitter, praising a "wonderful performance" and citing a "historic victory."

The outcome in Delhi was more complex, with the BJP victory after 15 years of Congress rule tempered slightly by a good showing for the anti-corruption Aam Aadmi party. Supporters of Aam Aadmi celebrated in the streets of the capital, brandishing brooms to symbolize a sweeping-out of corrupt politicians. The BJP was expected to be the largest party, but not to have an outright majority.

In Delhi, the Congress party came third - with chief minister of the capital, Sheila Dikshit, unseated.

There was a ray of sunshine for Congress in the state of Chhattisgarh, where the party had a slight lead in early counting. Congress is thought to have benefited from some amount of sympathy after much of its state leadership was killed in a Maoist militant attack there earlier this year.

The elections were held in the various states in recent weeks with counting delayed until Sunday. The tiny northeastern state of Mizoram is expected to report results from its election on Monday.

rc/tj (AFP, AP, dpa)