He said Yadav had already chosen a path which "leads to the RJD".
Regarding the claim of the supporters of Yadav that various state units of the party were against the alliance with the BJP in Bihar, he said the JD(U) was a recognised political party only in the eastern state.
"All the party MLAs and MLCs from Bihar are with us. They have reposed their faith in the chief minister and JD(U) president Nitish Kumar. A member or two cannot divide the party, all such claims of a split are false," said Tyagi.
He added that it was "shocking" that Yadav was "cosying up" to RJD chief Lalu Yadav, against whom he had fought "throughout his career".
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Tyagi said Rajya Sabha MP Ali Anwar Ansari was removed from the JD(U) parliamentary party because of "anti-party" activities.
"He (Ansari) has no moral right to attack us on the issue of joining hands with the BJP as he himself had been elected to the Upper House with the support of their MLAs," he added.
They met newly-appointed Rajya Sabha Chairman M Venkaiah Naidu and submitted a letter to him, announcing the appointment of Singh, a close aide of Kumar.
The JD(U) has 10 members in the Rajya Sabha. It had, last night, suspended Ansari from the parliamentary party for attending a meeting of opposition parties convened by Congress president Sonia Gandhi.
Differences between Kumar and Yadav surfaced after the former snapped ties with erstwhile Grand Alliance partners Congress and RJD and allied with the BJP to form the government in Bihar last month.
The former party president had claimed that the "real" JD(U) was with him and the one with Kumar was the "sarkari" JD (U).
Meanwhile, BJP president Amit Shah today said in a tweet that he had invited Kumar to formally join the NDA.
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