The BJP on Saturday attacked Bihar Chief Minister Nitish Kumar after a tape of an alleged conversation between RJD chief Lalu Yadav and jailed don-turned-politician Mohammad Shahabuddin was aired by a news channel.

Reacting to the conversation, senior Bharatiya Janata Party (BJP) leader and Union Law Minister Ravi Shankar Prasad described it as the worst form of "criminal-political nexus" in the country.

"Shahabuddin represents the worst form of criminal-political nexus in the country," Prasad said at a press conference here.

"A convicted notorious criminal like Shahabuddin is running the administration and Rashtriya Janata Dal (RJD) chief Lalu Prasad is assisting him in that," the BJP leader pointed out expressing his concern.

Daring the Bihar Chief Minister to act against his alliance partner, Prasad said: "I want to ask Nitish Kumar on behalf of the BJP -- will he institute criminal proceedings against Lalu?"

The Union Law Minister's remarks came after a new English news channel Republic TV on Saturday morning aired an audio clip of Shahabuddin and the RJD chief's alleged conversation.

Shahabuddin is also a former RJD MP from Siwan, his hometown, and former legislator from Siwan assembly constituency.

In the audio clip, the don-turned-politician was heard saying that "your SP (Superintendent of Police) is of no use" and Lalu was heard taking instructions from Shahabuddin over riots.

Prasad also said that it was a clear textbook case of "gross constitutional impropriety". 

"Nitishji, we want to know what you are going to say as the seniormost leader of your alliance has been found speaking to a notorious criminal over phone from jail, which is a crime?" the BJP leader said.

Firing a salvo at the opposition parties, Prasad said: "I also want to ask the political parties and leaders of the so-called secular brigade -- will you people make a deal with the criminals to fight against BJP?"

Shahabuddin, who is currently lodged in Delhi's Tihar Jail, is serving a life sentence after being convicted in over 10 cases. He was shifted to Tihar in February this year following a Supreme Court order. 

After coming out of jail in September last year, Shahabuddin had termed Lalu Prasad his leader and called Nitish Kumar as the "Chief Minister of circumstance".