The CBI has filed a fresh case against Lok Sabha MP Karti Chidambaram, son of former finance minister P Chidambaram, for allegedly facilitating visas of 250 Chinese nationals after receiving illegal gratification of Rs 50 lakh in 2011, officials said on Tuesday.

The CBI on Tuesday morning started coordinated search operations at 10 locations in multiple cities in the country, including Karti Chidambaram's residences in Chennai and Delhi, they said.

The searches are being conducted at three locations in Chennai, three in Mumbai and one each in Delhi, Karnataka, Punjab and Odisha, they added.

A CBI team also visited the official residence of Karti Chidambaram and senior Congress leader and Rajya Sabha MP P Chidambaram at Lodhi Estate here, the officials said.

"I have lost count, how many times has it been? Must be a record," Karti tweeted without specifying.

In the new case which is an offshoot of an ongoing probe, the CBI has alleged that Karti had received Rs 50 lakh alleged bribe to facilitate the visa of 250 Chinese nationals during the UPA regime for Talwandi Sabo power project in July-August 2011, when P Chidambaram was the Union home minister, the officials said.

It is alleged that the power project in Punjab for which establishment contract was given to a Chinese firm was running behind schedule and it needed manpower but there was a ceiling for allowing work permits of foreign nationals, they said.

It is alleged that the firm approached Karti who used his influence to facilitate the visas in violation of ceiling imposed, they added.

The CBI got the whiff of the case during an ongoing investigation against Karti who is already under probe in getting Foreign Investment Promotion Board (FIPB) clearance for the INX media and Aircel Maxis case, they said.

Following the scrutiny of the transactions, the CBI had detected the payments worth Rs 50 lakh which are alleged to be illegal gratification for facilitating the visa of Chinese workers who were supposed to work at the plant, the officials said.