"The MNS chief's diatribes against Biharis pose a challenge to all governments to deal with a person who has been holding out threat to the migrant people. People have the constitutional right to live and work in any part of the country," he told reporters in Patna.
"It is the duty of the central government and the government of the state (Maharashtra) to take note of the conduct of a person like Thackeray and deal sternly with such elements," Kumar said.
In Mumbai, Thackeray accused Hindi news channels of "distorting" his statement. "I want to tell the Hindi news channel to first understand the issue before it is broadcast...otherwise we know how to deal with it," he said.
Thackeray had on Friday threatened to brand Biharis as "infiltrators" and force them out of Maharashtra if authorities in Bihar take legal action against Mumbai policemen who picked up a teenager from there without informing their counterparts in that state.
Thackeray, whose party has often launched campaigns against Hindi-speaking people in Maharashtra, was reacting to a media report that Bihar chief secretary Navin Kumar has written to Mumbai police commissioner voicing displeasure over the arrest of the youth for vandalising the martyr's memorial during Azad Maidan protest on Aug 11.
Demanding strong action against the MNS chief, a visibly angry Kumar asked as to how the Centre and the Maharashtra government would deal with terrorism if they could not rein in a person like Thackeray.
"Has the Mumbai police and the Maharashtra government outsourced governance to Thackeray?" he asked.
On Thackeray's threat to declare Bihari migrants as "infiltrators" and drive them out of Mumbai and Maharashtra, Kumar said, "If he (Thackeray) challenges the Constitution and democratic rights of the people, then it is a challenge to all governments to deal with the brazen disrespect."
He said he will write to Prime Minister Manmohan Singh about it soon and demand action against the MNS chief.
Kumar said Maharashtra government and Mumbai Police have sought clarification on the protest letter written by Bihar DGP to the Mumbai police chief against the manner of arrest of the accused person, Abdul Qadir, from his native Sitamarhi district by Mumbai police without taking into confidence Bihar police.
Defending Bihar DGP's letter, he said as per the circular of the Union Home Ministry the police or investigating agency of any state was duty-bound to inform the local police and seek its cooperation in the arrest of an accused person in a case.
It was not done by Mumbai Police in the arrest of Qadir and several other accused persons from Bihar by police of other states, he said, adding Bihar government and its police were within their rights to protest the manner of such arrest.
The "lifting" of an accused person by the police of another state without intimation to local police cause law and order problems, Kumar said and demanded that the guidelines issued by the Union Home Ministry on it be adhered to by all state governments and investigative agencies, including police.
In Delhi, JD(U) president Sharad Yadav alleged that Thackeray was a "stooge" of the Congress which was using him against the Shiv Sena-BJP combine for electoral gains in the state.
"Raj Thackeray is a stooge of the Congress and the ruling party in the state is using him against the Shiv Sena-BJP combine," Yadav told reporters when asked about the MNS chief's remarks.