New Delhi, Mar 9 (IANS): The CBI on Friday sought further six-day custody of Karti Chidambaram to interrogate him for allegedly receiving kickbacks in getting foreign investment clearances to private companies when his father P. Chidambaram was the Finance Minister.

Additional Solicitor General Tushar Mehta told a special court here that the CBI had recovered a lot of documents proving that the senior Congress leader's son had direct links with Advantage Strategic.

The firm allegedly received lakhs of rupees from Aircel and INX Media for facilitating Foreign Investment Promotion Board (FIPB) approvals.

Mehta said the CBI raided an earlier unknown office of Advantage Strategic in Chennai on Wednesday and Thursday and "recovered a lot of documents proving Karti Chidambaram was directly associated with it.

"So we need six more days of police custody."

Defence lawyer Abhishek Manu Singhvi opposed the CBI plea, mocking at the agency for it failure to locate the registered office address of Advantage Strategic in Kumbukkan Road in Chennai.

"For one year, the CBI cannot find the registered office. Anyone can Google about it. It is tragic as well as comic for me."

Mehta countered Singhvi and said some documents had been shifted from the Chennai office location. The CBI raided the location on a tip off on March 7 and 8 and several documents were recovered, he said.

Singhvi said the CBI needed to rest its demand for extending the custody of his client on solid grounds. "You have no bonafide reason. It is a 10-year old case, documents cannot be changed, witnessed can be changed."

The CBI has alleged that Karti received kickbacks in the clearance of foreign investment worth Rs 305 crore for INX Media -- owned by jailed media executives Peter and Indrani Mukherjea.

It said it has a recorded statement of Indrani Mukherjea accusing Karti Chidambaram of demanding and receiving a bribe to get the FIPB clearance.

Karti Chidambaram was confronted with Indrani Mukherjea in Mumbai last week.

On Friday, the CBI moved two more applications, seeking court permission to confront Karti Chidambaram with his Chartered Accountant Bhaskar Raman.

The second is to allow the CBI bring the Mukherjeas to Delhi from Mumbai and identify the places where they met Kartik Chidambaram.

Singhvi also told the court that Karti's blood pressure levels were fluctuating as he was not allowed to sleep as four guards keep playing cards till 2.30 a.m. each night.

"On March 7, his blood pressure was 140/90 while on March 8 it was 150/100."

The court reserved its order on extending judicial custody till 4.30 p.m.