The EU’s finance commissioner, Pierre Moscovici, flies into Athens on Monday amid mounting political uncertainty following the Greek government’s abrupt decision to bring forward the presidential elections.

The Frenchman’s visit comes as the country’s radical-left opposition leader, Alexis Tsipras, steps up claims that Greece is being subjected to a campaign of “frenetic fear-mongering” not only by its Prime Minister Antonis Samaras but senior European officials ahead of this week’s ballot, the first of three polls.

“An operation of terror, of lies, is underway,” the leader of Syriza told supporters on Sunday. “An operation whose only aim is to sow terror among the Greek people and MPs, and to thrust the country ever deeper into the poverty and uncertainty of the memorandum,” he said referring to the EU-IMF-sponsored rescue programme to keep the debt-stricken economy afloat.

Tsipras was speaking after government leaders reiterated fears that Greece could be forced to exit the eurozone if parliament failed to elect a new head of state by 29 December. Should the ruling alliance lose the three-round race, the Greek constitution demands that general elections are called, a vote Tsipras’s party is tipped to win. “Everything is hanging by a thread … and if it is cut, it could lead the country to absolute catastrophe,” said the deputy premier, Evangelos Venizelos, whose centre-left Pasok party is junior partner in Athens’ two-party coalition.

In a re-run of the drama that haunted Greece at the height of the eurozone crisis in 2012, markets have tumbled with the country’s borrowing costs soaring on the back of revived fears of a Greek exit – called Grexit – if a Syriza-led government assumes power.

Moscovici, whose two-day visit is expected to focus on discussing stalled negotiations with the nation’s troika of creditors – the European commission, the IMF and the European Central Bank – will not be meeting Tsipras. Aides described the snub as “unbelievable”. Last week, the finance commissioner said he thought Samaras “knows what he is doing” and would win his gamble of expediting the vote for a new head of state. In an interview with Kathimerini on Sunday, he described the former EU environment commissioner Stavros Dimas, who is the government candidate for president, as “a good man.”

But the newly installed president of the European commission Jean-Claude Juncker, who is a close friend of Samaras, has gone further, warning of the perils of the “wrong election result”. “I wouldn’t like extreme forces to come to power,” he said of the poll’s potential to trigger early general elections. “I would prefer if known faces show up.”

Although it is not the first time that the politics of fear have been invoked to ensure that the twice bailed-out Greece toes the line, the flagrant intervention of figures so directly linked to Athens’ €240bn financial rescue programme has been quick to stir angry reaction abroad. Rushing to the support of Syriza on Saturday, the Party of the European Left, the continent’s alliance of leftist groups, deplored what it said was evidence of declining levels of democracy in the EU. “The pressure from the European commission on the electoral process of a sovereign country is unbearable, and raises serious questions about the future of democracy in Europe,” Pierre Laurent, the organisation’s president said in a statement posted on the party’s website.

Despite ever worsening levels of polarisation – represented by MPs who either grudgingly support or vehemently oppose the bailout programme – the majority of voters want the fractious parliament to elect a president so that early elections can be eschewed. A Kapa Research survey released at the weekend revealed that 57% want 73-year-old Dimas to assume the role but that 61.1% thought the ballot would fail.

Samaras signalled that he would rather go to a national vote than enter into a cross-party “salvation” government. Opinion polls show Syriza’s lead narrowing, fuelling speculation that it is unlikely it could win an outright majority.

A close aide to Samaras said the government believed it was in a “win-win” situation.

“Even if we lose [the vote for president] we will win because voters will blame Syriza for the chaos that will ensue,” he said. “And that will assure us victory in a national election.”