German government websites including Chancellor Angela Merkel's page were hacked on Wednesday in a cyber attack claimed by a group demanding that Berlin sever official ties with the Ukrainian government.
The attack, against which counter-measures were taken, had left the sites periodically inaccessible since 10 a.m., her spokesman Steffen Seibert said.
"Our service provider's data center is under a severe attack that has apparently been caused by a variety of external systems," he told a news conference when asked if Ukrainian hackers were responsible.
In a statement on its website, a group calling itself CyberBerkut took responsibility.
"CyberBerkut has blocked German Chancellor and the Bundestag's (lower parliamentary house) websites," it said on www.cyber-berkut.org.
The claim could not be independently verified.
Ukrainian Prime Minister Arseny Yatseniuk is due to meet with German President Joachim Gauck in Berlin later on Wednesday.