Nitish also declared that he is not in the race to become the Prime Minister in the 2019 Lok Sabha election and played down reports of a rift in Bihar's ruling Grand Alliance.
Describing his Janata Dal-United as "a small party", Nitish Kumar said,"I'm not capable of being PM nor do I have the aspiration for the post. My party is a regional party and I am not the face of 2019 general elections."
He said more than having a face, "the opposition should have alternative narratives to go to the people against the ruling party on key issues like the problem of farmers"
Nitish said he had said earlier that the Congress was a big party and it had every right to set the agenda and inform all the opposition parties.
The Congress should start work on an agenda only after approval from other opposition parties, he said.
"Opposition parties have to decide their role and they should start preparation for the 2019 Lok Sabha polls. But the opposition needs an alternative narrative, just a reactive narrative wont work."
Refuting reports of cracks in alliance of JD-U, the RJD and the Congress, Nitish said, "The Mahagathbandhan is intact."
Nitish also hinted that he was not happy with the Congress, which handled the Opposition's baton for the Presidential elections.
He said that the Opposition was so busy in the politics over the President election that it pushed farmers' unrest issue in the background, "which shouldn't be ignored at all".
In a reply to a question, Nitish Kumar said he did not attend the GST unveiling in Parliament because he was not invited.
"If I had got the invitation from the central government, I would have attended the GST meeting in Delhi."
He said the Goods and Services Tax regime was a good system and he had supported it since the beginning.
"Whatever issue is in the interest of the people and the country, I always support and always stand for it."
The Congress, which is a part of Grand Alliance in Bihar, is irked with Nitish after he extended support to the National Democratic Alliance (NDA) Presidential candidate Ram Nath Kovind.
Senior Congress leader Ghulam Nabi Azad launched an indirect attack on Nitish for the same and the JD(U) also reacted sharply.
On Sunday, it was reported that Nitish had held Congress responsible for the mess in the Opposition over the Presidential elections.
(With inputs from agencies)