Forza Italia leader Silvio Berlusconi gestures during a meeting in Rome, Italy, March 1, 2018. REUTERS/Alessandro Bianchi/File Photo

ROME (Reuters) - Silvio Berlusconi’s Forza Italia (Go Italy!) party on Friday accused the far-right League of breaking ranks with its conservative allies during a vote to select the speaker of the upper house Senate.

The clash between the two parties came on the first day of the new parliament following March 4 elections and could mark the premature end of the coalition that won the most seats in the national ballot but fell short of a working majority.

If the alliance collapses it will increase the possibility of a government made up of the League and the anti-establishment 5-Star Movement -- an option feared by markets because of their hostility to European Union budget rules.

In a toughly worded statement, Forza Italia accused the League of plotting for this outcome after the group said it would not vote for the pre-agreed conservative candidate for the prestigious Senate position.

The League’s move was “a hostile act ... which breaks the unity of the centre-right coalition and reveals the plan for a League/5-Star government,” Forza Italia said.

Tensions frequently surfaced between Forza Italia and the League during the election campaign but no one expected the alliance to rupture so soon after the vote.

Electing the speakers of the two houses is the first task of parliament and negotiations between the parties broke down on Thursday when 5-Star - the largest single party at the election - refused to back Berlusconi’s pick for the Senate job.

Berlusconi had backed Forza Italia veteran Paolo Romani, but the 5-Star Movement, whose appeal is based on a pledge to clean up politics, immediately rejected him because he has a conviction for embezzlement.

League leader Matteo Salvini sought to break the deadlock on Friday by saying his party would back another Forza Italia senator, Annamaria Bernini, but he did so without the consent of Berlusconi, prompting the unexpected rupture between the allies.