European Central Bank (ECB) President Mario Draghi addresses a news conference following the ECB's governing council's interest rate decision in Frankfurt, Germany, September 7, 2017. REUTERS/Kai Pfaffenbach

FRANKFURT (Reuters) - The European Central Bank’s president criticized on Thursday a proposal by the Estonian government to launch a state-managed digital currency, reaffirming instead that the euro was the only valid money in the euro area.

A rise in popularity in so called cryptocurrencies, which are normally issued by private companies and exist only in electronic form, has been worrying the ECB, which has said they could in theory erode its control over the supply of money.

Estonia became the first European country to openly discuss the prospect of a digital currency managed by the government and offered to the country’s more than 20,000 e-residents - foreign entrepreneurs who open a firm in the country via the web.

Mario Draghi’s comments come as the status of the euro is called into question in Italy, where an opposition party has proposed that the government issued small-denomination, interest-free bonds to pay suppliers as a way to circumvent a ban on currencies other than the euro.

“I won’t comment on the Italian intention but I will comment on the Estonian decision: no member state can introduce its own currency.” Draghi said in answer to a question during his regular press conference. “The currency of the euro zone is the euro.”

The idea for the ‘estcoin’ came from Kaspar Korjus, the head of Estonia’s e-Residency project. The Tallinn government is now seeking feedback online.