(Reuters) - NMC Health NMC.L is still trying to unravel details about the holdings of the company's top investors, it said on Friday after announcing that one of its controlling shareholders had resigned from the board.

FILE PHOTO: General view of NMC specialty hospital in Abu Dhabi, United Arab Emirates, February 11, 2020. REUTERS/Satish Kumar/File Photo

The largest private healthcare provider in the United Arab Emirates is listed in London on the blue-chip FTSE 100 index but has come under increasing pressure after shareholder Muddy Waters raised questions over its finances, prompting major investors to sell out, sending its share price tumbling.

On Friday NMC said that vice chairman Khalifa Butti Omeir Bin Yousef is stepping down from the board. His resignation came after UK regulators this week said they were looking into the company after news that founder and chairman B.R. Shetty had inaccurately disclosed the size of his stake in the business.

NMC subsequently said on Friday that there had been a series of complex shareholder dealings involving Shetty, Bin Yousef and another top investor, Saeed Butti Al Qebaisi.

The company said Bin Yousef and Al Qebaisi had notified them that some of their shares had been pledged as security for loans by Shetty in an arrangement “they were not party” to.

“The company continues urgently to seek clarity from Dr. B.R. Shetty, Khalifa Bin Butti and H.E. Saeed Bin Butti in relation to the above arrangements and their respective shareholdings,” NMC said.

The disclosure is likely to raise further questions about NMC’s governance and loans taken out by its top shareholders against their stock. Shetty on Monday said that he was stepping back from the board while a legal review of his shareholding disclosures continues.

Al Qebaisi and Bin Yousef on Friday said that an estimated 26 million of the 58.5 million shares they hold have been pledged against loans.

Shares in NMC were down 3.8% at 1351 GMT. The stock has slumped by 70% since Muddy Waters issued a report on Dec. 17 questioning the value of the company’s assets and reported cash balances.

NMC has denied Muddy Waters’ allegations and launched an independent review of its finances.

The company this week said it had received buyout interest from Italian-backed GKSD Investment Holding and United States-based KKR & Co KKR.N. GKSD subsequently confirmed it could bid for the hospital operator but KKR has said it would not.