News of the bank's latest offering came as bitcoin rallied to all-time highs.

Clients of Saxo Bank can now trade ethereum exchange-traded notes, as the lender deepens its foray into the burgeoning but controversial crypto-currency market. 

The Copenhagen-headquartered lender, which has a private banking operation, said in a statement yesterday that its clients now have the option to trade four ETNs that track Ether, a rival crypto-currency to bitcoin, which launched earlier this week. 

ETNs share traits with exchange-traded funds, but instead of giving investors exposure to a basket of assets or securities, they typically offer exposure to a single asset class. 

Saxo Bank also offers its clients access to two bitcoin-tracking ETNs. These and the new ethereum ETNs are listed on the Nasdaq OMX Stockholm Stock Exchange. 

“We have increasing client demand for exposure to crypto-currencies and I am very pleased that we can now offer clients exposure to both bitcoin and ethereum through exchange-traded notes,” said Claus Nielsen, head of markets at Saxo Bank. “Crypto-currency markets are still at an early development stage and we find that listed products like ETNs without leverage, offering high levels of transparency, are good ways to include crypto-currencies in our multi-asset product offering.”

CoinShares, the issuer of the ethereum ETNs, is headed by former JP Morgan trader Daniel Masters. His firm's products track the price of Ether Tracker One (COINETH:SS) and Ether Tracker Euro (COINETHE:SS). 

Nasdaq Stockholm is the only European exchange to offer exposure to crypto-based assets. 

CoinShares has been likened to BlackRock's iShares, but for crypto-currency investments, as it now has six professional-grade crypto-based investment vehicles, collectively valued at more than $300 million. 

Like bitcoin, the first and most well-known crypto-currency, ethereum has enjoyed soaring prices in recent months. The crypto-currency's price has surged more than 3,300 over the past seven months, rising from as little as $11 per coin to as much as £381, according to CoinDesk data. 

Ethereum was up 1.18 per cent at the time of writing (15:14, 12/10/2017), trading at $307.20.

Meanwhile, bitcoin's price rallied to an all-time high of $5,231.28 on Thursday, according to CoinDesk, spurred by rising investor interest as the crypto-currency recovered from recent headwinds. 

Bitcoin is up around 424 per cent year-to-date.