"Those who missed no opportunity to abuse each other are seeking support from each other," Paswan said in an apparent reference to Nitish approaching Lalu for the victory of two party nominees in Rajya Sabha bypoll.
Kumar earlier in the day had said he had telephoned the RJD chief seeking his support for JD(U) RS nominees.
Paswan, addressing a LJP function to felicitate party winners in the general election, said the coming together of the two would have no impact as they have been rejected by people in the recent Lok Sabha election.
"LJP alone has six MPs which RJD and JD(U) have together," he said, taking a potshots at his rivals.
In the 2014 Parliamentary election in Bihar, NDA won 31 seats including 22 of BJP, 6 LJP and 3 Rashtriya Lok Samata Party. RJD won 4 while Nitish Kumar's JD(U) slided to 2 from 20 it had in the previous election.
Launching a blistering attack on rivals, the LJP chief said despite their best efforts to pin down Narendra Modi over 2002 Godhra riots, the BJP-led NDA registered a resounding victory.
"I have been saying from the beginning that 12 years have lapsed since Godhra riots in 2002. But, rivals kept harping on the event to pin down Narendra Modi which did not yield any result among voters," he said.
"Despite 1984 anti-Sikh riots, people accepted a Prime Minister from Sikh community. Notwithstanding Emergency and responsible for 1990 Bhagalpur riots, people elected Congress to power in the past," he said to drive home his point. Paswan said that minority Muslims were supporting Narendra Modi government due to its commitment to development.