MUMBAI (Reuters) - The chief executive of India's Punjab National Bank (PNB) PNBK.NS met officials of the serious fraud office on Wednesday, as authorities widened a probe into a $2 billion fraud that has been billed as the country's biggest banking scam.

Sunil Mehta (2nd L), Managing Director and Chief Executive Officer of Punjab National Bank, arrives at the Serious Fraud Investigation Office (SFIO) amid a widening probe into a $2 billion fraud, in Mumbai, India, March 7, 2018. REUTERS/Francis Mascarenhas

Sunil Mehta’s appearance before the Serious Fraud Investigation Office (SFIO) follows its meeting with executives of at least two other banks on Tuesday.

PNB did not immediately respond to a request for comment on the SFIO probe.

In the fraud at PNB which was first disclosed by the bank in February, the lender and police have accused some bank employees of colluding with two jeweler groups which raised credit from overseas banks based on fraudulent guarantees issued by rogue PNB staff.

Police have also so far arrested 19 people including eight of PNB’s current and former employees, along with executives from jeweler Nirav Modi and his uncle Mehul Choksi’s companies.

Executives from private sector lenders ICICI Bank ICBK.NS and Axis Bank AXBK.NS met with the SFIO on Tuesday, according to sources with direct knowledge of the matter.

In a statement to the stock exchange late on Tuesday, Axis said the SFIO had sought information from it on the accounts of Nirav Modi and Choksi’s Gitanjali group of companies.

ICICI Bank also told the stock exchange on Tuesday its executives continue to “engage actively and provide requisite inputs” to investigative authorities, without commenting on Tuesday’s meeting.

Indian authorities including the Central Bureau of Investigation and the Enforcement Directorate have conducted extensive searches and questioned people in connection with the PNB fraud.

Both Choksi and Modi have denied the allegations and lawyers for the two key accused PNB employees in the case have also said they are innocent.

A source and documents reviewed by Reuters on Tuesday showed the amount involved in the fraud is likely to rise beyond the $2 billion mark.

Shares in Punjab National Bank PNBK.NS fell as much as 3.9 percent on Wednesday, tumbling for a fourth straight session. PNB has lost more than 40 percent of its market capitalization since disclosing the fraud last month.