Russian nationalists claimed on Tuesday to have hacked into and disabled the official website of Ukrainian President Viktor Yushchenko in a retaliation cyber attack.
A group called the Eurasian Youth Union, whose leader is banned from Ukraine for having vandalised Ukrainian national symbols, said it had acted because its own website had come under attack by Ukrainian authorities.
Attacks against Yushchenko's website -
www.president.gov.ua- began on Sunday and were continuing on Tuesday, the president's press office said, without identifying the suspected hackers.
The press office said it had registered 18 000 separate cyber attacks against the website coming from Britain, Israel, Kazakhstan, Russia, Ukraine and the United States.
"Yushchenko's official website will not work unless Kiev stops its attacks against the official website of the Eurasian Youth Group," the group said in a statement quoted by Interfax news agency.
Leaders of the Eurasian Youth Group were banned from travelling to Ukraine earlier this year after they claimed to have vandalised Ukrainian national symbols on a mountain in the west of the country.