The price of bitcoin is approaching $40,000 once again after Tesla CEO Elon Musk tweeted that was having active discussions with bitcoin miners regarding the sustainability of the digital coin.

Bitcoin was trading around $38,767.62 at 3:30 a.m. ET on Tuesday and its price has risen over 9% in the last 24 hours, according to data from CoinDesk.

Almost all of the other major cryptocurrencies are also higher.

Ethereum’s price has risen more than 15% in the last 24 hours to $2,634.79, while Dogecoin has seen its price rise more than 8% to 35 cents a coin.

A small handful of less well-known cryptocurrencies such as Tether and Dai have seen their price fall in the last 24 hours, but the declines are negligible.

Bitcoin, the world’s most popular cryptocurrency, jumped minutes after Musk tweeted: “Spoke with North American Bitcoin miners. They committed to publish current & planned renewable usage & to ask miners WW to do so. Potentially promising.”

The coin initially popped 4% to hit $39,824.81 a few hours later, before falling back to almost $38,000. 

Microstrategy CEO Michael Saylor followed up on Musk’s tweet, saying he hosted a meeting between the Tesla CEO and some bitcoin miners that led to the formation of the Bitcoin Mining Council, which will promote sustainability.

Bitcoin mining requires vast amounts of energy. As a result, bitcoin has a carbon footprint comparable to that of New Zealand, producing 36.95 megatons of CO2 annually, according to Digiconomist.

Musk has been a big supporter of cryptocurrencies, sparking rallies in the prices of digital coins, including bitcoin, several times in the past year. His tweets and comments around cryptocurrency often send the prices soaring or plunging.

In an SEC filing in February, Tesla revealed that it bought $1.5 billion worth of bitcoin and would accept it as a form of payment. The company later said it registered a net gain of $101 million from sales of bitcoin during the quarter, helping to boost its net profits to a record high in the first quarter.

However, Musk’s relationship with the digital coin appeared to change earlier this month. He tweeted on May 12 that the company “suspended vehicle purchases” using bitcoin, out of concern over “rapidly increasing use of fossil fuels” for bitcoin mining.

Bitcoin’s rally this week comes after turmoil in the crypto markets that saw its price fall below $32,000 on Sunday.

Last week’s crypto sell-off came after authorities in China and the U.S. moved to tighten regulation and tax compliance on cryptocurrencies.

Chinese authorities called for tighter regulation on crypto mining and trading on Friday, and the U.S. Treasury announced Thursday that it would require stricter crypto compliance with the IRS.

— Additional reporting by CNBC’s Jessica Bursztynsky.