Speaking to ANI here, Tyagi said that the decision to nominate Kumar as prime ministerial candidate was discussed at a meeting of the party on Monday.
"I think Nitish Kumar is suitable for the post, but it is up to our members to decide who could be the next Prime Minister," Tyagi said.
The JD (U) currently has two seats in the Lok Sabha and Bihar offers a total of 40 seats in the lower house.
With the Rashtriya Janata Dal (RJD) and Congress as alliance partners, Nitish could increase his tally for the upcoming 2019 elections.
The two parties are in a grand alliance with Lalu Yadav's RJD in Bihar and the latest proposition is an attempt to form a similar affiliation for UP where the ruling Samajwadi Party is on a wobbly track and the BJP is fast gaining ground post its phenomenal 2014 Lok Sabha poll performance.