NEW DELHI • India's Central Bureau of Investigation (CBI) has searched the homes of former finance minister P. Chidambaram and his son, in a probe into suspected criminal misconduct related to approvals of investment deals.

The dawn raids yesterday marked an escalation in pressure by federal investigators against Mr Chidambaram, a senior leader of the opposition Congress party who has been a vocal critic of Prime Minister Narendra Modi.

The CBI, India's main federal crime-fighting agency, carried out searches at locations in the cities of Mumbai, Delhi, Gurugram and Chennai, including the residence of Mr Chidambaram's son, Karti, there.

The raids were "in connection with criminal misconduct" in granting approval for foreign investment deals, a CBI spokesman said without giving further details.

A police report obtained by Reuters that lays out the case named Mr Karti Chidambaram as one of those accused of criminal conspiracy, cheating, seeking to influence a public servant and criminal misconduct.

Mr P. Chidambaram denied wrongdoing. He said all investment approvals granted during his tenure were above board.

"The government, using the CBI and other agencies, is targeting my son and his friends," he said in a statement.

"The government's aim is to silence my voice and stop me from writing," said Mr Chidambaram, who writes a weekly column for The Indian Express.

"All I will say is, I shall continue to speak and write."

Mr Chidambaram, 71, served twice as finance minister in the Congress-led coalition that ran India for a decade - from 2004 to 2008 and then from 2012 until the party's election defeat at the hands of Mr Modi's Bharatiya Janata Party (BJP) in May 2014.

The case against Mr Karti Chidambaram spells out alleged violations of India's foreign investment law in the approval in 2007 of the sale of stakes in a company called INX Media to offshore entities.

Also named in the case are Peter Mukerjea, at the time head of strategy at INX, and his wife, Ms Indrani Mukerjea. The couple, once a fixture on the Mumbai party circuit, are now on trial and charged with murdering Ms Mukerjea's daughter from a previous relationship.

Mr Karti Chidambaram, addressing a media scrum outside his home in Chennai, said there was no evidence to back the claims against him, adding they were politically motivated.

The case marks a new twist in a legal onslaught against Mr P. Chidambaram, who has been the target of litigation brought by a senior BJP lawmaker alleging the approval of a separate telecoms deal in 2006 was corrupt.

Mr Chidambaram said that neither he nor Foreign Investment Promotion Board officials were suspected of wrongdoing in the hundreds of cases it had reviewed while he was in office.

"There is no allegation against any of them. There is no allegation against me," he said.

"Every case was processed according to law and approval was granted or refused in accordance with the recommendations of the FIPB," he said.

REUTERS