By Lidia Kelly and Jan Strupczewski
WARSAW/BRUSSELS (Reuters) - Poland said on Tuesday it would oppose the re-appointment of its former prime minister Donald Tusk next week as the chairman of EU leaders, in a move that highlights the increased isolation of the nationalist Polish government in Europe.
Tusk heads the European Council, which brings together the leaders of the 28 member states of the European Union, and his term ends in May. The Council chair will play a crucial role, among other things, in Britain's negotiations to exit the EU.
Tusk, a smooth-talking centrist, has wide backing among EU leaders for a second term except from his own country, where the Law and Justice party (PiS) of his arch-rival Jaroslaw Kaczynski now holds power.
"Donald Tusk is a politician who breaks the elementary rules of the European Union," Kaczynski told a news conference in Warsaw.
"Someone who breaks such rules simply cannot be the European Council's president and cannot under any circumstances count on our support - or a lack of our objection," he said.
Kaczynski holds Tusk "morally responsible" for the death of his twin brother, President Lech Kaczynski, in a plane crash in Russia in 2010, when Tusk was Poland's prime minister. Polish and Russian investigations blamed pilot error for the crash.
EU leaders usually pick the Council chair by unanimity but could do so by majority vote if necessary - a scenario diplomats said was now likely when the leaders decide the issue next week.
TUSK IS "DONE DEAL"
"Everybody is supporting Tusk and it is only Poland that is making difficulties," one senior EU official said.
Several other diplomats in Brussels echoed that view.
"It is a done deal, Tusk will get re-appointed next week - by majority, if not unanimously," another senior diplomat said.
EU leaders believe Tusk has proven himself in handling of issues such as Greece's economic woes, the bloc's migration crisis or Brexit.
Malta, which holds the EU's rotating six-month presidency, will oversee the process of choosing the Council chair.
"There is only one official candidate so far," a spokesman for the Maltese presidency of the EU said.
"Everybody is ... scratching their heads in disbelief (over Warsaw's stance). It just shows that Poland and its leader Kaczynski are completely out of touch with European politics," the first senior EU official said.
The eurosceptic PiS government is already at loggerheads with Brussels over the rule of law and democratic standards in Poland following a slew of changes to the constitutional court and a tightening of control over state media.
PiS officials have floated the possible candidacy of a Polish member of the European Parliament, Jacek Saryusz-Wolski, as an alternative to Tusk. That option has been largely dismissed by EU diplomats and officials in Brussels.
"The candidacy of Jacek Saryusz-Wolski is completely unrealistic," said Tomasz Siemoniak, deputy head of the Civic Platform, the main opposition party in Poland which Tusk led for many years.
"I believe this speculation is closely linked to the domestic situation in Poland, in terms of weakening the image of Tusk and showing that other options have been pursued."
(Additional reporting by Pawel Sobczak in Warsaw and Gabriela Baczynska in Brussels; Editing by Gareth Jones)