Ukrainian hackers hostile to the government claimed Thursday to have launched a cyber attack against the websites of Poland's presidency and the Warsaw Stock Exchange.
The hacker group Cyber Berkut said it blocked the sites, both down on Thursday afternoon, in response to what it said were Poland's actions as "sponsors of fascism in Ukraine".
"Our western neighbour on orders from Washington renders political, diplomatic and military assistance to nationalists and oligarchs who destabilise and wreck Ukraine," the group alleged on its website.
They accused Poland of sending mercenaries to Ukraine, allegations already levelled by Moscow and firmly denied by Warsaw.
Named after "Berkut", the now-disbanded Ukrainian riot police unit used against pro-West protesters earlier this year in Kiev, the group has a history of unleashing virtual warfare over the country's crisis.
The hackers shut down three of NATO's websites for several hours in March after the defence alliance came out in support of the new, pro-Western government in Kiev.
The group said at the time it would "not allow a NATO presence on the territory of our homeland".
The conflict in eastern Ukraine between pro-Russian rebels and government forces has resulted in more than 2,000 deaths in four months, the UN human rights agency said Wednesday.
An ex-communist country and member of the European Union since 2004, Poland has expressed concern over Russia's actions in the region and political backing for Ukraine's pro-Western government.
Explore further: Ukraine war already in full swing in cyberspace