Mumbai: A special CBI court here on Sunday issued non-bailable warrants (NBWs) against diamantaire Nirav Modi and his uncle Mehul Choksi in connection with Rs 13,500 crore Punjab National Bank (PNB) fraud.

The court's move comes following Central Bureau of Investigation (CBI) request as both the diamond traders, who left the country in January, refused to join the investigation in cases related to the scam.

Meanwhile, the CBI continued questioning the officers of overseas branches of Indian banks that extended alleged credit facilities on the basis of Letters of Undertaking (LoUs) issued by the PNB to firms related to Modi and Choksi-- the promoter of Gitanjali Group.

The CBI said "the officer who dealt with forex transactions in Allahabad Bank's Hong Kong Branch, has been summoned from Hong Kong and is being questioned".

Modi, a regular on the lists of rich and famous Indians since 2013, along with his group companies -- Diamond R US, Stellar Diamond and Solar Exports, and uncle and business partner Choksi and others have been named in the huge scam, admitted by the PNB in February and leading to a massive upheaval in the country's banking system.

The issuance of NBWs by a court also opens door of seeking Red Corner Notices against both of the accused from the Interpol.

Earlier, a lookout notice was issued by the CBI against Modi and Choksi. However, Modi and his associates fled the country before the notices were issued. While Modi and his brother Nishal left India on January 1, his wife Ami, a US citizen, and Choksi left on January 6, all before the CBI received a complaint from the PNB on January 29.

On Friday, the CBI questioned the Reserve Bank of India former Deputy Governor Harun Rashid Khan, between 2011 and 2016, in connection with the PNB bank fraud and relaxation of 80:20 gold import scheme brought by then Union Finance Minister P. Chidambaram on May 13, 2014, barely three days before the counting of votes of 2014 general election.

He was asked about the lapses in the statutory audit of the central regulator due to which the PNB fraud remained undetected for a long time as the SWIFT messaging system was misused.

The PNB has claimed in different complaints to the CBI that several LoUs -- issued by one bank to other banks, based on which foreign branches offer credit to buyers -- were fraudulently issued by its officials in connivance with Modi and the other accused in the case causing huge losses to the bank.