In a landmark ruling on Tuesday, the EU's top court declared that the "Safe Harbor" agreement did not sufficiently guarantee the protection of Europeans' personal data.

The accord, signed in 2000 between Brussels and Washington, enabled companies and international networks to easily transfer personal data to the United States without having to seek prior approval, a potentially lengthy and costly process.

"Europe's high court just struck down a major law routinely abused for surveillance," Snowden tweeted on Tuesday, adding that "we are all safer as a result."

Snowden, a former US National Security Agency (NSA) contractor, was granted asylum in Russia after exposing mass surveillance by the NSA in 2013.

"This is the second time in as many years the world has relied upon CJEU (the Court of Justice of the European Union) to defend digital rights. Thank you Europe," he wrote.

'Milestone' in online privacy

Snowden also congratulated Austrian privacy campaigner Max Schrems who launched the case against Facebook following Snowden's revelations two years ago.

The law student challenged Irish authorities over user data transferred to the US from the social network's European base in Ireland.

In a statement released shortly after Tuesday's decision, Schrems said it a "milestone when it comes to online privacy."

He noted, however, that that the ruling doesn't bar data transfers from the EU to the US, but rather allows national data protection authorities to review individual transfers.

Nevertheless, the verdict will drastically affect US tech giants such as Facebook and Google, who will find it considerably harder to store private data belonging to EU citizens.

White House spokesman Josh Earnest said there are concerns about the economic consequences of the decision.

"We are disappointed that the court has struck down an agreement that since 2000 has proved to be critical in protecting both privacy and fostering economic growth in the United States and the European Union," Earnest said.

Facebook's European operations are based in Ireland, but the company said it had nothing to fear from the European cour ruling.

"This case is not about Facebook," a spokesperson said in a statement, noting that the social media giant "relies on a number of the methods prescribed by EU law to legally transfer data to the US from Europe, aside from Safe Harbor."

ksb/jr (Reuters, AFP, AP, dpa)