Malta-based cryptocurrency exchange OKEx has announced that it is adding four U.S. dollar-pegged cryptocurrencies to its platform for trading.

Rolling out the new additions over Monday and Tuesday, the exchange said in a support notice that it will list TrustToken's TrueUSD (TUSD), Circle's USDCoin (USDC), the Gemini Dollar (GUSD) from the Winklevoss-founded New York exchange and Paxos Standard Token (PAX).

The latter three tokens were all launched by their respective companies in September, while TrustToken was ahead of the pack with a March release.

At press time, OKEx is the fifth-largest exchange by volume for bitcoin, and the third-largest for the tether stablecoin, according to data from CoinMarketCap.

The OKEx listing news comes as controversy over the most commonly used stablecoin, tether (USDT), is only building.

Confidence in the token – which is widely used by traders and exchanges to quickly move funds without the need to convert back into U.S. dollars – has been fading in recent months over the perception that USDT developer Tether LLC and its sister firm, crypto exchange Bitfinex are not transparent over the actual amount of USD being held to back the stablecoin.

Some exchanges have already moved to drop tether, and the recent launching of new alternatives may only increase that likelihood.

In other related news, a major sell-off in tether early today saw the price of bitcoin surge to its highest level for a month as its premium on Bitfinex climbed to around $600 over the global average at one stage this morning.

With the sell-off, Tether fell to an 18-month low of $0.925284 at 07:00 UTC, according to CoinMarketCap data. At press time, USDT had returned to $0.962815.

OKEx said it will start accepting deposits in the four new stablecoins from 17:00 local time today (09:00 UTC), with spot trading in pairs against bitcoin and tether to start Tuesday at 14:00 HKT (06:00 UTC). Withdrawals in the newly listed tokens will commence three hours later.

In a similar statement, crypto exchange FCoin said it would add the same stablecoins to its platform, though it did not provide a timeline.

Correction: This article has been amended to correct an error that indicated OKEx is based in Hong Kong. It is now based in Malta.

OKEx app image via Shutterstock