Indian Prime Minister Manmohan Singh Monday rejected accusation by the opposition that the Congress-led government is misusing the country's prime investigation organ, the Central Bureau of Investigation (CBI), as a "mouthpiece."

"CBI is not Congress bureau of investigation. CBI is not mouthpiece of Congress," Singh said here.

Singh also called for smooth functioning of the Parliament and said that the House was ready for discussions on the issue of arrest of former Gujarat minister Amit Shah.

"We are here to debate many issues of national importance. The government is ready for every piece of discussion that the opposition may want," he said.

"We want the Parliament to function smoothly. That is what the people of India expect."

Turbulence is expected as the Monsoon session of the Parliament is to begin this week.

The opposition is accusing the government of a series of policy mistakes and failures.

The opposition Bharatiya Janata Party (BJP) has alleged that the Congress-led United Progressive Alliance (UPA) government was behind the arrest of former Gujarat Minister of State for Home Amit Shah.

Amit Shah was arrested in connection with the 2005 Sohrabuddin Sheikh staged shootout case.

"There is no truth in that. The Opposition knows that jolly well. Sohrabuddin Sheikh is Supreme Court-directed case. The central government has no role in it," Singh stated.

"The government is ready for every piece of discussion in Amit Shah's case," he added.

Sohrabuddin Sheikh was a terrorist from whose premises in Indore AK-47s were recovered. He used to operate an inter-state gang.

Shah was arrested Sunday and remanded to judicial custody for his role in the alleged fake encounter case.

The 46-year-old former minister was produced before a special court which remanded him in judicial custody till Aug. 7. He resigned as the Minister of State for Home Saturday.

Earlier in the day, Shah, who has been charged with kidnapping and murder of alleged gangster Soharabuddin Sheikh and his wife Kausar Bi in 2005, made a dramatic appearance before a media meet at the BJP state headquarters and refuted all allegations against him, saying, the charges were "fabricated and politically motivated."

"I have full faith in the judiciary and I am sure the allegations against me will be cleared by the courts. The incident happened five years back. But the CBI acted in such haste that they did not even give me enough time to reply. I will respond to all the charges and will expose the people who are behind bringing of these allegations," he said, before going to surrender to the CBI.

According to the CBI chargesheet, Shah had entrusted the task of eliminating Sheikh, an alleged gangster, to a couple of police officials who are also in custody.