The CBI Thursday questioned Congress MP Karti Chidambaram for nine hours in connection with an alleged scam pertaining to the issuance of visas to 263 Chinese nationals in 2011 when his father P Chidambaram was home minister, officials said.

A special court had ordered Karti to join the CBI investigation within 16 hours of his arrival from the UK and Europe, where he had gone with the permission of the Supreme Court and the special court.

The MP returned from his trip on Wednesday, and arrived at the CBI office around 8 this morning to answer questions related to the case.

Speaking to reporters outside the CBI headquarters, Karti said the case against him was "bogus", and claimed that he had not facilitated the issuance of visa to any Chinese national.

He was allowed to go for a recess for about an hour in afternoon after which the questioning resumed. The MP was quizzed till about 6 pm.

Coming out of the intense questioning, Karti Chidambaram said it all was a political vendetta, and that he would depose again if the agencies call him.

The case pertains to the allegations of Rs 50 lakh being paid as bribe to Karti and his close associate S Bhaskararaman by a top executive of Vedanta group company Talwandi Sabo Power Ltd. (TSPL), which was setting up a power plant in Punjab, for re-issuance of project visas for 263 Chinese workers of a firm company which was executing the project, the CBI FIR said.

The agency has already taken Bhaskararaman in custody in connection with the case.

Karti Chidambaram has denied all allegations, saying "if this is not harassment, not a witch-hunt, then what is".

The CBI has alleged Makharia, a representative of the power company, approached Karti through his "close associate/front man" Bhaskararaman, officials said.

"They devised a back-door way to defeat the purpose of ceiling (maximum of Project visas permissible to the company's plant) by granting permission to re-use 263 Project visas allotted to the said Chinese company's officials," Joshi said.

Makharia allegedly submitted a letter to the home ministry seeking approval to re-use the project visas allotted to this company, which was approved within a month and permission was granted to the company, the officials said.

It has been further alleged that the payment of the said bribe was routed from Talwandi Sabo to Karti and Bhaskararaman through Mumbai-based Bell Tools Ltd camouflaged as payment of false invoice raised for consultancy and out of pocket expenses for Chinese visas related works, the CBI FIR said.

"... Whereas the private company based at Mumbai was never in any kind of work relating to visas rather it was in an entirely different business of industrial knives," Joshi said.