Writing in its bog, Vole said a group it nicknamed "Strontium" was using seven internet domains as part of an effort to spy on government bodies and think tanks in the EU and the United States, as well as Ukrainian institutions such as media organisations.

Strontium is Microsoft's moniker for a group others often call Fancy Bear or APT28 - a hacking squad linked to Russia's military intelligence agency.

The Russian Embassy in Washington did not immediately return a message seeking comment, but following its normal line it would probably deny it or blame the Ukrainians.