The White House, in an unusual public statement, said on Thursday that there would be undisclosed “international consequences” for an alleged June 2017 Russian military cyber attack against Ukraine that spread to infect networks and computers globally.

Military website Defense One reported that when a senior US national security official was queried on what “consequences” meant and whether the cyberattack’s impact was greater than previously disclosed, the official replied, “We are not going to forecast our moves.”

A White House statement on Thursday said: “In June 2017, the Russian military launched the most destructive and costly cyber-attack in history. The attack, dubbed ‘NotPetya,’ quickly spread worldwide, causing billions of dollars in damage across Europe, Asia, and the Americas. It was part of the Kremlin’s ongoing effort to destabilize Ukraine and demonstrates ever more clearly Russia’s involvement in the ongoing conflict. This was also a reckless and indiscriminate cyber-attack that will be met with international consequences.”

The British government reportedly issued a similar statement several hours after the White House released its statement.

Defense One said the consequences alluded to could include a retaliatory cyberattack by the US or sanctions. “The latter of which would eventually have to be announced, the former, not so much,” the website said.

‘NotPetya’ refers to a worldwide cyberattack that began on June 27, 2017. Companies in the Ukraine were reportedly the first to be attacked using a previously unknown variant of  so-called Petya encrypting ransomware. Infections were said to have spread to France, Germany, Italy, Poland, UK and the US. However, the bulk of the infections targeted Russia and Ukraine, where more than 80 companies were initially attacked, including the National Bank of Ukraine.