Bitcoin is tumbling

It's a rough start to the week for bitcoin. The cryptocurrency trades down 10.11% on Monday, at $2,275 a coin, a one-week low.

The action seems to be a continuation of the selling that developed on Wednesday, when rival Ethereum flash-crashed from $296 to 10 cents before recovering its losses.

Bitcoin is down about 16.6% since Wednesday's opening print.

The recent weakness in bitcoin follows a run-up of more than 200% to start the year. Bitcoin's 2017 gains have been propelled by heavy buying from China and Japan.

Recent strength has come on the heels of China's three biggest exchanges resuming withdrawals for the first time since February, and Japan naming bitcoin a legal payment method in early April. Additionally, Russia's largest online retailer began accepting bitcoin, even though Russia has said it wouldn't consider the use of the cryptocurrency until 2018.

But the gains have created some skepticism as of late. The billionaire Mark Cuban called bitcoin a "bubble" as the cryptocurrency hit its then-all-time high on June 6.

"I think it's in a bubble. I just don't know when or how much it corrects," Cuban tweeted. "When everyone is bragging about how easy they are making $=bubble."

About a week later, Goldman Sachs' head of technical strategy, Sheba Jafari, said bitcoin was looking "heavy" and could drop as low as $1,915 before seeing a rally. It put in a low of $2,076 before rallying to almost $2,800.

There remains one big unknown. In March, the US Securities and Exchange Commission rejected two bitcoin exchange-traded funds. It has since taken public comment on its decision about an ETF proposed by the Winklevoss twins, but it has not made an additional ruling.

Bitcoin is up 136% in 2017.