Rashtriya Janata Dal (RJD) chief Lalu Prasad today admitted that his decision to break away from the Congress-led alliance and ally with Ram Vilas Paswan's Lok Janashakti Party was the "biggest mistake" that resulted in his party's "heavy" defeat in Bihar.

The RJD supremo himself lost the Pataliputra parliamentary constituency to his nearest JD(U) rival Ranjan Prasad Yadav, while he just managed to win at Saran against BJP rival Rajiv Pratap Rudy.

''It was the biggest mistake. And there is no doubt that breaking away from Congress has resulted in our heavy defeat," Lalu Prasad said, adding, ''People have rejected our alliance with Ram Vilas Paswan. We were not expecting this result.''

"It's the mandate for the people,'' Lalu said, adding that he has no grudges against Bihar chief minister Nitish Kumar. ''We will now assess why we lost in Bihar and what went wrong,'' he added.

Both Lalu and Paswan said they were happy that secular parties have won and people have rejected the Bhartiya Janata Party.

The Congress party has won the mandate and we congratulate them, he added.

Meanwhile, Ram Vilas Paswan lost his Hajipur seat to JD(U)'s Ram Sunder Das.

"As far as Bihar is concerned, you have your wins and misses. I have served people. Nobody can say that Paswan has not worked for Hajipur. I had done for the development of the constituency whatever I could have done. Despite all these works you lose, it is just the wish of the people. I will continue to serve them," he said, adding that he will continue to serve the people of Hajipur. 

Bihar chief minister Nitish Kumar claimed the Lok Sabha election results should be seen in conformity with the mandate that the NDA got in the last assembly polls.

''The people of Bihar have rejected negative politics pursued by RJD president Lalu Prasad and LJP chief Ramvilas Paswan and have given a positive vote to my government which has been successful in bringing about peace, communal harmony and development,'' Nitish Kumar said.

According to latest trends, the JD(U) was leading in 32 of 40 seats.

The RJD chief, however, did not rule out going back to the Congress.  "Ram Vilas Paswan and I will go to Delhi on Sunday and will decide then,"  said Lalu Prasad.