BRUSSELS: The European Union on Thursday voiced support for the United States over cyber attacks it has suffered, including a major hack blamed on Russia, as Washington imposed sanctions on Moscow.

"The European Union and its Member States express their solidarity with the United States on the impact of malicious cyber activities, notably the SolarWinds cyber operation, which, the United States assesses, has been conducted by the Russian Federation," the EU's foreign policy chief Josep Borrell said in a statement.

"The compromise affected governments and businesses worldwide, including in EU Member States," he added.

The statement on behalf of the 27-nation bloc insisted that "all actors must refrain from irresponsible and destabilising behaviour in cyberspace".

"We will continue to investigate malicious cyber activities with a view to sustained, joint and coordinated action to prevent, discourage, deter and respond to such malicious behaviour," it said.

The US announced economic sanctions against Russia on Thursday and the expulsion of 10 diplomats in retaliation for what Washington says is the Kremlin's US election interference, the massive SolarWinds cyber attack and other hostile activity.

President Joe Biden's executive order "sends a signal that the United States will impose costs in a strategic and economically impactful manner on Russia if it continues or escalates its destabilising international action," the White House said.