The group called 'CyberBerkut' claimed the attacks, saying it wanted to protest against Ukraine Prime Minister Arseniy Yatsenyuk's visit to Berlin.
It was able to block access to the websites of the federal press office, the chancellery, the Bundestag -- the lower house of the parliament -- and the foreign ministry for several hours with its Denial of Service (Dos) attack, in which servers are flooded with traffic until they collapse.
The group, in a statement, demanded that Germany should not provide any political or financial support to the "criminal regime in Kiev, which is engaged in a bloody civil war" in eastern Ukraine.
Yatsenyuk is visiting Berlin seeking Germany's "financial assistance to continue the fighting," the statement said. "The conflict in eastern Ukraine had already cost thousands of people their lives and with German money more people will be killed," it said. The statement appealed to the German government and the public "not to support the bloody civil war any longer."
This was the first time that the German government and parliament were subjected to a cyber attack of such a dimension, according to media reports. A government spokesman said the attack began at around 10 am local time.
While access to the Bundestag website was restored in the afternoon, the website of Merkel's office and the federal press office were still blocked even after seven hours.
The government has initiated measures to counter the attacks, the spokesman said.
Yatsenyuk began his visit by holding discussions with President Joachim Gauck. He is scheduled to meet Merkel on Thursday. They are expected to explore possibilities to resolve the conflict in eastern Ukraine.
Continuing dispute with Russia over its role in the conflict and a meeting of the leaders of Russia, Ukraine, Germany and France planned for January 15 in Astana, Kazakhstan, will also figure in their discussions.
In March last year, the group claimed responsibility for shutting down three NATO websites in a series of denial of service attacks.

Latest News from World News Desk