BRUSSELS Poland's Prime Minister Beata Szydlo said on Thursday that she would block the joint statement that normally follows a meeting of European Union leaders after they overrode her objections to re-electing the summit chair.
She said this would mean the summit was invalid, but EU officials said this was not the case.
Szydlo said walking over the Polish opposition deepened divisions in the bloc and undermined key EU principles.
"If we fail to rebuild these principles of respect for every member state, the EU will be faced with crises for many years," she told a news conference.
Szydlo made the comments after Donald Tusk, her compatriot but political foe, was given a second term to chair the EU summits by all the other 27 EU states despite Poland's objections.
Diplomats said that Tusk's reappointment would not be prevented even if Warsaw blocked the summit conclusions.
(Reporting by Gabriela Baczynska and Jan Strupczewski; editing by Philip Blenkinsop)