Kumar had reached Delhi on Saturday.
The Rashtriya Janata Dal chief Lalu Prasad, who arrived in Delhi on Sunday, said he will be meeting leaders on the alliance issue.
The Janata Dal-United chief Sharad Yadav, who had on Thursday asserted that the RJD, JD-U and the Congress party will fight the Bihar assembly polls together, is already back in the national capital having rounds of negotiations with leaders of other parties in Bihar.
The top leaders of the RJD and the JD-U are expected to hold back to back meetings in the national capital to thrash out differences soon.
The leaders are likely to hold a meeting at the residence of Samajwadi Party chief Mulayam Singh Yadav as well to resolve the Bihar alliance issue.
The SP chief was chosen by the six splinter groups of the Janata Parivar, including these parties, to work out their grand merger plan to take on a resurgent BJP, which has made deep inroads into their vote banks in Bihar, Uttar Pradesh and even Haryana.
The issue of merger of the six parties is for the time being slowed down with the focus shifting on first firming up the alliance for Bihar, the cradle of social engineering.
Amid speculation over the alliance, JD-U President Sharad Yadav had on Thursday asserted that his party will fight the Assembly polls together with the RJD and the Congress to challenge the BJP.
Just days before, there was a bitter war of words between leaders of the JD-U and the RJD amid speculation that the RJD chief was not keen to project Nitish Kumar as the chief ministerial candidate of the alliance.
The RJD vice-president Raghubansh Prasad Singh, who had openly expressed his reservations against declaring Kumar as the chief minister candidate of the alliance outraging the JD-U, later appealed to Congress President Sonia Gandhi to hammer out a solution and give shape to the anti-BJP alliance in Bihar.
The leaders from the two parties are expected meet the Congress leadership here as well but time is yet to be finalised.
Under one of the seat-sharing formulae that are being discussed, both the RJD and the JD-U could contest 100 seats each while 43 could be left for the Congress, the Communist Party of India-Marxist, the CPI and the Nationalist Congress Party.
The Bihar assembly has 243 seats.