Central Bureau of Investigation (CBI) on Tuesday arrested Vipul Ambani and four other senior executives of Nirav Modi and Mehul Choksi companies in the Rs11, 400 crore PNB fraud case that continued for six years.

Modi allegedly cheated the state-run bank by using fake bank "letters of understanding" (LoUs) to get loans. Most of the letters were sent to overseas offices of Indian banks, which made the actual loans, said Sunil Mehta, Punjab National Bank's managing director.

The PTI reported that Modi sent a letter to the bank this week saying he owes less than half the amount claimed by the bank in connection with the alleged fraud.

Nirav runs an international jewellery empire that reaches from India to New York, with a string of high-end brands. He and his family fled India weeks before the bank registered a criminal case with the CBI on 31 January, 2018.

The CBI and other Indian investigative agencies searched dozens of offices and residences used by Modi and his business partners. The bank named Modi, his brother Nishal Modi, wife Ami Modi and uncle Mehul Chinubhai Choksi as suspects in its complaint.

In his letter to the bank, Modi said he owes about Rs 5,000 crore (USD 775 million), according to PTI. He said the Rs 11,400 crore cited by the bank had resulted in a media frenzy that pressured authorities to quickly search and seize assets from his Firestar International and Firestar Diamond International companies.

"This thereby jeopardized our ability to discharge the dues of the group to the banks," Modi said.

With media reporting that Modi and his family were hiding in New York or Dubai, the external affairs ministry said it has suspended the passports of Modi and his uncle Choksi for four weeks.

It said in a statement that if they fail to explain within seven days why their passports should not be cancelled, their travel documents will be revoked.