Investing.com -- Binance, the world's largest cryptocurrency exchange, has temporarily suspended client withdrawals of Bitcoin, Chief Executive Changpeng Zhao said via Twitter on Monday.

Zhao blamed a "stuck transaction," which he said would take around 30 minutes to resolve. However, Zhao's first tweet was followed by another, half an hour later, saying that: "Likely this is going to take a bit longer to fix than my initial estimate." He promised more updates "soon."

The suspension comes only hours after Celsius Network, one of the world's biggest crypto lenders, suspended withdrawals due to what it called "extreme market conditions."

Celsius' news sent crypto enthusiasts rushing to get their money out, pushing Bitcoin down as much as 13% to its lowest in 18 months. Altcoins, such as Ethereum, Cardano, Solana and Dogecoin suffered even bigger losses. By 8:35 AM ET (1235 GMT), Bitcoin was trading at $24,211, down 12.2% on the day.

Zhao added his habitual reassurance that "Funds are SAFU."

The acronym SAFU stands for Secure Asset Fund for Users (SAFU), which is an emergency insurance fund established by Binance in July 2018 to protect users' funds. Binance seeded the fund with a percentage from its trading fees, hoping to build a reserve that would ensure the protection of user deposits.

The Secure Asset Fund was valued at $1 billion based on the opening price on January 29, 2022. The value of the fund, however, fluctuates based on market conditions, as it is held in Bitcoin and in Binance’s own BNB tokens. At current market prices, they are worth just over $410 million.