Outflows from Binance accelerated to $6bn in the first half of this week, while accounting firm Mazars has halted its work on crucial “proof of reserves” reporting, as the crypto exchange battles to avert a crisis of confidence.

Binance, which suffered $1bn outflows in a single day on Tuesday, is battling to reassure investors of its financial strength following the collapse of rival crypto exchange FTX.

The exchange said on Friday that it had been hit by roughly $6bn in net withdrawls between Monday and Wednesday.

Mazars had produced “proof of reserves” reports for Binance and other exchanges, including Crypto.com and KuCoin, as they rushed to persuade nervous clients that they hold sufficient assets to match all customer deposits.

However, the accounting firm said on Friday that it had “paused its activity relating to the provision of proof of reserves reports for entities in the cryptocurrency sector due to concerns regarding the way these reports are understood by the public”.

According to communications seen by the Financial Times, the level of media focus on the matter was also a factor in Mazars’ decision.

The willingness of auditors such as Mazars to issue proof of reserves reports has been a key factor in soothing nervous investors as crypto exchanges seek to prevent “run on the bank” scenarios of the kind that sank FTX, which is alleged to have fraudulently made off with customer assets leaving a multibillion-dollar shortfall in client funds.

The reports are far more limited in scope than a traditional audit of a company’s accounts, including its liabilities, and are much less robust.

To prepare a proof of reserves report, an auditor uses procedures agreed with the company but does not vouch for whether those procedures are appropriate. The auditor also does not give any assurance or opinion over the numbers in the report, as it would in a full financial audit.

Mazars’ decision to halt work on proof of reserves reports was not driven by specific financial problems at any of the companies, said a person briefed on its decision. The firm’s work was so limited that it had “not looked that much” into the financial position of the companies.

Some people at Mazars feared that despite caveats in its reports the firm was “lending credibility to a very volatile sector” and felt it had been “naive” and “silly” to take on the work, the person added.

Binance said the Mazars report was “additional validation” that the exchange’s assets were equal to or greater than its liabilities to customers.

“Over the past week, Binance passed a stress test that should give the community extraordinary comfort that their funds are secure,” the exchange said on Friday, adding that it was able to fulfil recent withdrawals “without breaking stride”.

Binance has said it holds more than $60bn in assets, enough to honour withdrawals. The company’s disclosures do not include its liabilities, which makes it difficult to ascertain its financial health.

In a recent interview with CNBC, Binance’s chief executive Changpeng Zhao refused to confirm whether the exchange would be able to finance a potential $2.1bn clawback from FTX in the event that funds were requested as part of FTX’s bankruptcy proceedings.

“We are financially OK,” said Zhao, adding that he would leave such issues to Binance’s lawyers.

On Friday, Binance re-emphasised its plans to deliver proof of reserves to its customers but did not commit to a timeline.

“We have reached out to multiple large firms, including the Big Four, who are currently unwilling to conduct a proof of reserve for a private crypto company and we are still looking for a firm who will do so,” the exchange said.

“We embrace additional transparency and we are looking into how best to provide those details in the coming months,” Binance added.

However, some auditors are sceptical of the crypto industry’s commitment to transparency.

Following the collapse of FTX, Paul MacIntosh, EY’s US financial services crypto co-leader, said on LinkedIn that proof of reserves reports do not assess companies’ internal controls, “which ultimately was the downfall of FTX”.

“To move to true transparency and trust in the industry requires a much bigger step up,” he said, calling for the industry to invest in better accounting systems, IT controls and independent corporate governance.

Several audit firms have said they had elevated some or all of their crypto-related clients to the status of “high risk”, triggering more thorough work that will take longer and lead to higher bills.

KuCoin said it was aware of Mazars’ decision and was “open to work[ing] with any leading and reputable audit[or]”.

Crypto.com said it would “continue to engage with reputable audit firms in 2023 and beyond”.

Both KuCoin and Crypto.com said they had provided customers with the ability to verify their own holdings individually online.