Italy's 5-Star Movement has chosen investigative television journalist Milena Gabanelli as its candidate for the presidency following an online vote by supporters, the anti-establishment party has announced.

The election of a successor to President Giorgio Napolitano, whose term ends on May 15, is a vital step towards resolving a stalemate after February's inconclusive election left no party able to form a government.

The next president's first task will be to find a way out of the deadlock, either by persuading the parties to come to an accord or by calling new elections. The choice of the head of state has caused fierce political wrangling.

The two houses of parliament, along with delegates from the regions, will start voting tomorrow, a process that may involve several rounds. No clear favourite has emerged.

The nomination of Gabanelli, a well-respected journalist from state broadcaster RAI, but a complete outsider to traditional politics, is unlikely to shift the battle between the centre-left alliance led by Pier Luigi Bersani and Silvio Berlusconi's centre-right bloc.

However, it ends speculation that the 5-Star Movement could back former prime minister Romano Prodi, who is strongly opposed by Mr Berlusconi but supported by elements of the centre-left.

In 5-Star's online consultation of its members, Mr Prodi came eighth on a short-list of 10 selected in a preliminary ballot.

Mr Prodi, an ex-president of the European Commission, is among the names most frequently mooted in the media as a possible president but Mr Berlusconi has rejected supporting one of his oldest political rivals as head of state.

The other name most often spoken of is former prime minister Giuliano Amato, who is well-known outside Italy for his handling of a financial crisis in 1992 but is handicapped by his image as a member of the traditional political elite, now widely distrusted in Italy.

The head of state has an important, broadly defined political role in overseeing government.