Blockchain, one of the biggest cryptocurrency wallets in the world, launched a service to buy and sell digital coins in the U.S. on Thursday, in a challenge to Coinbase.

The U.K.-headquartered company already allows its British customers to buy and sell bitcoin via its service, and is now launching the function in one of the biggest cryptocurrency markets in the world.

From Thursday, Blockchain's U.S. users will be able to sell their bitcoin, with the buying function coming at a later date.

Many users in the U.S. have complained about services that offer cryptocurrency trading, citing issues around being able to withdraw money or get liquidity. Given that backdrop, Peter Smith, CEO of Blockchain, said it's better to start with just offering a sell service as it helps to control the launch in the U.S. and make sure people have a good experience.

"If we are prioritizing short-term gains, we would prioritize buy — that is what most people have done. But it's really time to make sure we nail that experience," Smith told CNBC in an interview ahead of the launch announcement.

The launch followed a huge sell-off in major cryptocurrencies that began Tuesday. The market appeared to stabilize on Thursday, however.

Blockchain claims to have 22 million users and Smith said that it has 1 million daily users. Thirty percent to 40 percent of those are in the U.S., Smith added. In comparison, Coinbase, which has seen a surge in sign-ups to its platform in recent months, has over 10 million users, according to its website. Coinbase allows people to buy and sell bitcoin, ethereum and bitcoin cash.

Smith said that "in a few weeks" Blockchain will add other cryptocurrencies to its platform to buy and sell.

Cryptocurrencies have divided opinion among business leaders and experts. J.P. Morgan CEO Jamie Dimon famously called bitcoin a "fraud", while noted investor Warren Buffett told CNBC that cryptocurrencies will "come to a bad ending."

But others have said bitcoin will continue to climb this year. Julian Hosp, co-founder of TenX, a firm that wants to make it easier for people to spend virtual currencies, told CNBC in December that bitcoin could hit $60,000 in 2018, but could crash first. And Dave Chapman, managing director of cryptocurrency trading firm Octagon Strategy, said that bitcoin could hit $100,000 in 2018.

Blockchain's Smith did not give a price call on bitcoin, but said that it's likely the cryptocurrency's dominance, which is already on the decline, could continue to fall.

"What could happen this year is that I think we will see the dominance of bitcoin as a percentage of the market capitalization go down. That could be because other digital coins get strong, or that there are a lot more that are interesting," he said.