Tens of thousands of people have gathered in the centre of the Macedonian capital Skopje to demand the resignation of conservative Prime Minister Nikola Gruevski.
The protest on Sunday follows the release of a massive cache of wiretapped conversations by the head of the opposition Social Democrats, Zoran Zaev.
The conversations purport to reveal corruption at the highest levels of government, including mismanagement of funds, spurious criminal prosecutions of opponents and even attempted cover-ups of killings.
Zaev said the conversations were leaked to him by "patriots" in the domestic intelligence service. He demands the formation of a caretaker government that will organise new elections, the Associated Press news agency reported.
Crowds, including members of Macedonia's ethnic Albanian minority, thronged the central avenue in front of Gruevski's government office, angry over a flood of damaging wire-tap disclosures that Western diplomats say have cast serious doubt on the state of democracy in the ex-Yugoslav republic.
Refusing to resign, the conservative leader has called his own rally for Monday, stoking fears of confrontation in the country of two million people 14 years after it narrowly avoided all-out civil war during an ethnic Albanian insurgency.
Gruevski has rejected the accusations.