BRUSSELS (Reuters) - The European Union threatened sanctions on Thursday against Macedonian politicians who it says have obstructed efforts to end a long-running crisis after a push for EU-mediated talks failed.

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Macedonia, a poor Balkan country on the frontline of the migrant crisis, has been in turmoil since the opposition accused then Prime Minister Nikola Gruevski and his counter-intelligence chief in February 2015 of wiretapping more than 20,000 people.

Under an EU-brokered agreement, Macedonian politicians agreed last year to appoint a special prosecutor to investigate the scandal and to hold early elections, but the process is on the brink of collapse.

The EU is willing to consider travel bans and asset freezes against politicians judged to be blocking progress, said an EU official involved in the mediation, speaking on condition of anonymity.

The official said that Macedonia faced being shunned on the world stage unless its political leaders made a concerted effort to end the 14-month-old crisis, which deepened last week when President Gjorge Ivanov drew protests by pardoning 56 officials over the wire-tapping scandal.

“We are extremely concerned by the short-sightedness of the current government. The EU is willing to consider sanctions on politicians blocking a resolution of the crisis. Macedonia is heading toward international isolation,” the official said.

EU Enlargement Commissioner Johannes Hahn and three members of the European Parliament, who have acted as mediators, earlier admitted the failure of their efforts to bring Macedonian political leaders together for talks in Vienna on Friday.

Macedonia’s opposition Social Democrats said they would only take part in the Vienna talks if Ivanov annulled the pardons.

They also want June 5 elections postponed until a free and fair vote can be held. They have pledged to boycott the election if it goes ahead.

The EU official said Ivanov must now annul the pardons as a pre-requisite for more EU-brokered talks. “That is the number one priority. Only then can we go back and talk,” he said.

In a statement, Hahn and the other EU mediators said Macedonia must take urgent steps to ensure the elections were credible and could be recognized by the international community. The crisis could hinder Macedonia’s attempts to join the EU and NATO, they said.

“We deeply regret retrograde steps that move the country further away from its aspirations toward European Union accession. In the absence of any further progress, we are now forced to consider further actions,” they said.

Steps Macedonia must take to prepare credible elections include updating its voter list, the EU official said.

The United States and other countries have called on Ivanov to reconsider the pardons. Ivanov has stood firm, although he has said that any politician who had received a pardon could ask for it to be overturned in his or her individual case.