ROME (Reuters) - The decision of Italy’s ruling League party not to back Ursula von der Leyen as the next European Commission president risks isolating the country, Deputy Prime Minister Luigi Di Maio said on Thursday in the latest sign of coalition friction.

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Di Maio is the leader of the League’s government partner, the 5-Star Movement, which voted in favor of von der Leyen, a German conservative who takes the helm of the Commission, the EU executive, in November.

The clash within Italy’s ruling coalition over the EU vote could endanger Rome’s hopes of securing a top job in the new EU executive, political sources said.

“The League’s attitude risks isolating Italy in Europe”, the deputy prime minister said.

The League, led by Matteo Salvini, emerged as the country’s largest party in May’s European elections, and Italian Prime Minister Giuseppe Conte has said that it was up to it to pick the country’s commissioner.

Rome hoped to obtain the competition portfolio with League bigwig Giancarlo Giorgetti seen as a front runner.

In a video posted on Facebook, Di Maio said the antitrust job was important. “...It would allow us to stop a number of shameful cases against Italy, cases of state aid which prevent us from helping companies,” he said.

Italy has clashed with the current competition chief Margrethe Vestager, most notably over state-driven rescue plans for struggling banks. However, any designated commissioner is not supposed to put national interests above EU directives.

The League has accused 5-Star of betraying national interests by voting for von der Leyen, but Di Maio hit back saying that the ruling partner was fighting for getting a seat rather than for a political idea.

“We backed her because she wants to implement the minimum salary,” Di Maio told state-owned broadcaster RAI 1, adding that the League decided not to support her because she did not give them guarantees over an eventual role in the commission.

The clash over the EU vote is not the sole cause of tension between the two ruling parties. Media allegations that the League sought illegal funding from Russia have also generated friction, with the 5-Star and the opposition parties calling on Salvini to address parliament over the scandal.

However, Di Maio made clear he did not believe the League had received cash from Moscow. “If I had the slightest suspicion that the League had taken money from Russia, I would not be in government with them”, he said.

The Russia case is the subject of a criminal investigation. Salvini has repeatedly denied any wrongdoing and there is no evidence that a deal was struck.