A row over Poland's attempt to oust European Union President Donald Tusk threatens to overshadow a summit this week that was meant to focus on post-Brexit unity.
Warsaw's surprise announcement of a challenger has upset plans to rubber-stamp a new mandate for former Polish premier Tusk, and underscored east-west splits in the 28-nation bloc.
The leaders are also at odds over the contents of a declaration they hope to make on the future at a summit in Rome later this month marking the EU's 60th birthday.
Big guns like Germany and France back a "multi-speed Europe" in which some members could deepen integration faster than others, but Eastern nations oppose it.
"President Tusk believes that the key message in Rome should still be unity," a senior EU official told a briefing ahead of the summit on Thursday and Friday.
"Indeed if in Rome a new baby is to be born, the name of this baby should be Unity rather than Multi-speed," added the official, who spoke on condition of anonymity.
Unity is at a premium for the EU as it deals with Britain's departure after last year's referendum, Russian aggression and new US President Donald Trump.
- 'Very many' back Tusk -
The first task for the leaders on Thursday, when they will meet at 28 with Britain included, will be deciding on a new term for Tusk until the end of 2019.
Poland's eurosceptic government threw a spanner in the works on Saturday when it suddenly proposed Euro-MP Jacek Saryusz-Wolski instead of Tusk, its long and bitter foe.
Centrist Tusk is still near-certain to be re-elected as he has broad support for his handling of crises including migration and Greek debt.
So far Poland has only the support of Hungary -- led by the populist, anti-immigration Viktor Orban -- for a change.
"Mr Tusk enjoys the confidence of very, very many," German junior foreign minister Michael Roth said in Brussels on Tuesday.
"And this is a clear signal that should be understood as well by those who still have a problem with a reappointment of Donald Tusk as president of the Council."
EU officials added that Poland has no veto on the matter. Under EU rules it would need a majority of at least 72 percent of the 28 leaders, representing at least 65 percent of the EU population.
But there is disquiet at the way an internal political feud has spread to the European stage at a time when it is meant to be giving the impression of unity.
"I think we will leave our Polish friends to face the cold wind alone," an EU diplomat told AFP on condition of anonymity.
Tusk has been at odds with Law and Justice for years, especially its chief, Jaroslaw Kaczynski, who accuses him of "moral responsibility" for his twin brother and then-president Lech Kaczynski's death in a 2010 plane crash in Russia.
- Rome declaration -
The Tusk issue highlights a growing split between the older, western EU nations and the poorer, newer countries in the East, especially on issues such as migration.
This is also likely to figure when 27 EU leaders meet without Britain on Friday to discuss the March 25 summit to mark the 60th anniversary of the EU's founding Treaty of Rome.
The "big four" EU economies -- Germany, France, Italy and Spain -- said at a meeting in Versailles on Monday that they supported a multi-speed Europe choosing at which speed they integrate on issues like defence and the economy.
"Unity does not equal uniformity," French President Francois Hollande said after the talks.
But Eastern European nations have strongly opposed any such move.
Germany's Roth indicated that there were problems with drafting the declaration, saying "I am anything but satisfied with the current state of preparation."
He echoed Slovakian premier Robert Fico who said last week that said preparations for Rome were "pathetic".
Meanwhile the EU leaders will also discuss a fresh challenge in the form of instability and growing Russian activities in the Western Balkans.
The EU leaders are likely to warn in a statement against "external destabilising influences" but Moscow itself will not be specifically named, diplomats said.