Patna, Aug. 12: The Janata Dal United, RJD and the Congress today formally sealed a grand alliance in Bihar under which the parties of Nitish Kumar and Lalu Prasad will contest in 100 seats each.

The Congress will be given 40 of the 243 seats, setting the stage for a straight contest against the BJP-led NDA in the Assembly elections expected later this year.

The NCP, which has been given the remaining three seats, has threatened to quit the alliance. NCP leader Tariq Anwar said the party had called a meeting to decide its course of action.

"Our alliance has taken a clear shape now. We have also identified the seats," Bihar chief minister Nitish announced. Lalu Prasad and C.P. Joshi, the AICC general secretary in charge of Bihar, flanked Nitish at the news conference.

Nitish said the grand alliance would organise a joint rally at Gandhi Maidan here on August 30 to unveil its agenda and reply to Narendra Modi who has been on a "relentless spree" to denigrate Bihar by describing it as "Bimaru (ailing)" and " abhaga (luckless)".

While Nitish and Joshi were guarded in their comments, Lalu Prasad said: "This Narendra Modi, instead of offering pinda to his ancestor at the holy city of Gaya (on August 9), used cheap language for Biharis and Bihar leaders. We will give him a resounding reply through our rally here on August 30."

The Prime Minister, too, is scheduled to address a rally in Bihar - at Bhagalpur - on August 30.

Lalu Prasad said that after the rally on August 30, the partners would carry out joint campaigns. "The BJP benefited by the division of votes between Nitish and I. The ploy will not work again. We are united and one this time around," he said.

Asked how he would defend his "rule-of-the-law" plank with Lalu Prasad in his company, Nitish said: "We have to give no explanation. It is the BJP that has to do all the explaining.... What happened to their promises to the people?"