SARAJEVO (Reuters) - European Commission chief Jean-Claude Juncker told Bosnia’s divided leaders on Wednesday they must overcome their differences and work closely together if they want their country one day to join the European Union.

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Juncker, who is touring the Western Balkan nations, received from the Bosnian officials a completed questionnaire on the country’s readiness to join the EU. They hope it will help lead to Bosnia gaining the status of an EU candidate later this year.

“I cannot promise you a date for when your country becomes a candidate,” Juncker, speaking in French through an interpreter, told the Bosnian political establishment assembled for the handover ceremony. “The essence is more important than the date.”

“It requires joint efforts for a state to become a member,” he later told lawmakers in the national parliament. “When there are differences, it leads to paralysis, it leads to delays.”

After the bloody breakup of Yugoslavia in the 1990s, Bosnia was split into two highly autonomous regions - a federation of Muslim Bosniaks and Croats and the Serb Republic. They are linked via a weak central government that includes a three-member inter-ethnic presidency.

Bosnia applied for EU membership 18 months ago but after some initial progress political quarrels among its rival Orthodox Serb, Catholic Croat and Muslim Bosniak leaders have stalled the reform process.

It took 14 months for its multiple administrations to agree responses to more than 3,000 questions relating to the compatibility of Bosnia’s economic, legal and social systems with EU standards.

“I am sorry to see that many regard this process as a technical one when it is rather about accession to a way of living together,” Juncker said. “This is a political project and for this we need you to unify forces in this country.”

Juncker urged the lawmakers to agree on changes to the election law which are seen as crucial for the formation of governments after a national election in October, warning that without them, progress on the EU path will be endangered.

He also called on Bosnia to tackle organized crime and corruption, and to resolve its all territorial conflicts.

“We cannot import instability... Democracy does not exist without compromise,” Juncker added.

Bosnia, along with Kosovo, is the last in the queue of the EU aspirants in the Balkans and hopes to catch up with other countries that are at a more advanced stage of integration, including Albania, Macedonia, Montenegro and Serbia.

The ex-Yugoslav republics of Croatia and Slovenia are already EU members.