Guy Verhofstadt | Jeff Pachoud/AFP via Getty Images Guy Verhofstadt declares bid for Parliament presidency Liberal makes his intentions known as Socialists dismiss ‘under-the-table deal.’

Guy Verhofstadt, a former Belgian prime minister who leads the Alliance for Liberals and Democrats in Europe, officially declared his candidacy for president of the European Parliament Friday.

Verhofstadt's Liberals are a far smaller group than those of the two leading candidates: Antonio Tajani of the European People's Party and Gianni Pittella of the Alliance of Socialists and Democrats. But neither Tajani nor Pittella can clinch the presidency without a coalition involving the smaller parties.

Verhofstadt had proposed a deal with Pittella, in which he put himself forward as the candidate of a left-leaning coalition, but Pittella angrily rebuffed the overture. His party issued a statement Thursday declaring that it "excludes any possible under-the-table deal."

That statement sets the stage for an all-out-brawl for the 376 votes needed to win the presidency and succeed Martin Schulz, of the Socialists, who is returning to Germany to seek a seat in the Bundestag.

Under a previously agreed-upon power sharing arrangement, the presidency was due to pass to the center-right EPP group, but that deal went up in smoke after Schulz's announcement that he was leaving.

Pittella announced that he would no longer participate in the "grand coalition" that European Commission President Jean-Claude Juncker, a member of the EPP, has relied on in the first two years of his term.

Underscoring Pittella's intention to take a more aggressive stance toward the EPP, the S&D group issued a statement Friday calling for a broader inquiry into potentially illegal tax breaks, including in Luxembourg, where Juncker was prime minister for more than two decades. Juncker has repeatedly faced criticism over his potential role either in allowing sweetheart tax deals for some corporations or looking the other way as officials in Luxembourg approved them.

While Verhofstadt represents a smaller group, as a former prime minister and now chief Brexit negotiator for the Parliament he is a more prominent figure than either Tajani, a Parliament vice president and former adviser to ex-Italian Prime Minister Silvio Berlusconi, or Pittella, a longtime MEP.

In an email announcing his candidacy, Verhofstadt said: "I am convinced that the ongoing play off between the two big groups is not in the interest of the Parliament nor of the Union. This is the time for a candidate with a proven ability to lead a broad coalition and who can unite the pro-European forces in this house, putting the interest of the European citizens first."

Along with the email he issued a manifesto and a video in support of his candidacy.