The charter _ which has been almost a decade in negotiations _ has been ratified by 26 of the bloc's 27 member nations, with only the Czech leader yet to sign.

Czech President Vaclav Klaus is asking for opt-out from the treaty's Charter of Fundamental Rights, a text that sets out liberties citizens enjoy under EU law, over worries of property claims by ethnic Germans stripped of their land and expelled after World War II.

Slovak Foreign Minister Miroslav Lajcak said his country needs similar assurances, as both nations were part of the former Czechoslovakia when it expelled about 3 million ethnic Germans.

The demand issued during talks by EU foreign ministers further complicates negotiations among EU envoys on how to get the EU treaty approved as soon as possible. The treaty streamlines decision-making and adds key posts like an EU president to boost the bloc's global influence.

It remains unclear how Slovakia's concerns could be addressed, as it has already signed and ratified the treaty. Other EU member states are also loathe to change the treaty's complex legal text, for fear they may be forced to go through the arduous national ratification process again.

"Slovakia is an equal successor to the former Czechoslovakia as the Czech Republic, and therefore we have to insist on the same level of political and legal protection," Lajcak said.

Czech officials are continuing talks over the demands with envoys from Sweden, which will chair a two-day summit of EU government leaders starting Thursday in Brussels.

Sweden had hoped to have the treaty fully approved by the summit's opening so EU leaders could appoint the bloc's new EU president and foreign policy chief, but that seems unlikely, Sweden's EU affairs minister Cecilia Malmstrom said.

She said the WWII laws Klaus is concerned about are "not in any way" threatened by the new treaty's rights charter.

"We are of course in contact with him and the Czech government in order to try to make him sign," Malmstrom said.

The Czech Constitutional Court is also deliberating on whether the treaty complies with the country's constitution.