Three Adani group companies have pledged additional shares for State Bank of India (SBI), a key lender to the Indian conglomerate whose listed entities have lost more than $100 billion in market value after a scathing report by a US short seller.

Adani Ports and Special Economic Zone, Adani Transmission Ltd and Adani Green Energy Ltd pledged shares to SBICAP Trustee Co, the firm said in filings to the Bombay Stock Exchange on Friday.

The trustee, a unit of India's biggest state lender SBI, said it had pledges for shares worth 1 per cent of Adani Ports, up from 0.65 per cent, for 0.55 per cent of Adani Transmission, up from 0.44 per cent, and for 1.06 per cent of Adani Green, up from 0.68 per cent.

The additional pledges are part of a $300 million letter of credit - issued by a bank to another bank as a guarantee for payments made - provided by SBI for Adani group's Carmichael coal mining project in Australia, a statement from SBI said.

The collateral is reviewed at the end of each month to assess if it needs to be topped up on account of any mark-to-market losses, SBI said in a statement.

Listed companies controlled by billionaire Gautam Adani have lost more than $100 billion in market value since January 24, when US short seller Hindenburg Research accused the conglomerate of stock manipulation and improper use of offshore tax havens.

The group has rejected the allegations and denied any wrongdoing.

SBI said top-ups of share pledges were also done twice last year and the latest was undertaken on Feb. 8 2023.

SBI's total exposure to the group was 0.9% of its loan book, or around 270 billion Indian rupees ($3.3 billion), Chairman Dinesh Kumar Khara has said.

"Such a share pledge is only as additional collateral security over and above the project assets and no additional finance is extended by SBI against such shares pledged,” the SBI statement said.

India's market regulator, the Securities and Exchange Board of India, is investigating the Adani group's links to some of the investors in the conglomerate's aborted share sale, sources told Reuters on Friday.

Fitch estimates that loans to all Adani group entities account for 0.8 per cent to 1.2 per cent of total lending by Indian banks rated by the agency.

The Adani exposure of Indian banks is not enough to affect their credit profiles, two global rating agencies have said.