The European Parliament's website was unavailable for several hours on Wednesday due to a denial-of-service attack by "Pro-Kremlin" hackers, after its lawmakers designated Russia a state sponsor of terrorism, the institute's president said.
The parliament's website was up again shortly after 1700 GMT, around two hours after the institution had reported the outage.
"The European Parliament is under a sophisticated cyberattack. A pro-Kremlin group has claimed responsibility," European Parliament President Roberta Metsola said in a tweet shortly after the website went down.
"This, after we proclaimed Russia as a State-sponsor of terrorism. My response: SlavaUkraini (glory to Ukraine)", she said.
The outage was caused by a distributed denial of service (DDoS) attack, which works by directing high volumes of internet traffic towards targeted servers in a relatively unsophisticated bid by so-called "hacktivists" to knock them offline.
These attacks usually don't cause much damage.
A spokesperson for the parliament did not immediately respond to questions regarding any damage.
Earlier on Wednesday, lawmakers voted to declare Russia a state sponsor of terrorism, arguing Moscow's military strikes on civilian targets such as energy infrastructure, hospitals, schools and shelters violated international law.
The move is largely symbolic, as the European Union does not have a legal framework in place to back it up. At the same time, the bloc has already imposed unprecedented sanctions on Russia over its invasion of Ukraine.
(Reporting by Bart Meijer, Sabine Siebold and James Pearson; editing by Foo Yun Chee and Bernadette Baum)
