A smartphone displays the Tether market value on the via The Crypto App. Guillaume Payen | SOPA Images | LightRocket | Getty Images

Major digital currencies edged higher on Monday as tether, a controversial token designed to be pegged to the U.S. dollar, fell more than 2 percent. The price of bitcoin, ether and XRP — collectively the three biggest cryptocurrencies by market value — rose by around 7 percent higher, according to data from industry website CoinMarketCap. Bitcoin was within touching distance of $7,000 at around 8 a.m. London time. The rise in virtual currency prices follows a sharp downturn last week, where the market shed billions of dollars in market capitalization, in tandem with a two-day sell-off in global stock markets. Tether, a token that its creators claim is 100 percent backed by fiat currency reserves, was seen trading 2.5 percent lower at $0.965 Monday morning. Earlier in the morning, the digital asset fell to around 93 cents. The firm behind it, Tether Limited, has come under scrutiny over whether it actually holds enough reserves to match the amount of tether tokens in circulation — Tether claims it does.

"There is concern about tether and whether it is truly backed by dollars and rumors about USDT (tether) being delisted from various exchanges," Charles Hayter, the chief executive of comparison site CryptoCompare, told CNBC in an email. Hayter also pointed to a report by an industry publication that Bitfinex, a cryptocurrency exchange connected to tether, had suspended deposits in U.S. dollars, euros, sterling and Japanese yen. "We would like to reiterate that although markets have shown temporary fluctuations in price, all USDT in circulation are sufficiently backed by U.S. dollars (USD) and that assets have always exceeded liabilities," Leonardo Real, Tether's chief compliance officer, said in an emailed statement to CNBC. "In June 2018, a report from Freeh Sporkin & Sullivan, LLP (FSS), based on a random date balance inspection and a full review of relevant documentation of bank accounts, confirmed that all tethers in circulation as of that date were indeed fully backed by USD reserves." Bitfinex was not immediately available for comment when contacted by CNBC. Tether is what is known in the industry as a "stablecoin," a cryptocurrency pegged to a government-backed currency to avoid the volatility common in cryptocurrencies like bitcoin. The idea has also been put into practice by Goldman Sachs-backed firm Circle.