REUTERS/ GETTY The United States has backed Italy's referendum

FREE now and never miss the top politics stories again. SUBSCRIBE Invalid email Sign up fornow and never miss the top politics stories again. We will use your email address only for sending you newsletters. Please see our Privacy Notice for details of your data protection rights.

Italian Prime Minister Matteo Renzi gave the go ahead for the vote on constitutional reform which will allow Italians to vote on restricting the powers of the senate. The bold move has been seen as a political gamble by many Italians but the US has backed the Prime Minister. John Phillips, US ambassador to Italy, warned saying no to the referendum "would be a step backwards for foreign investments in Italy”.

Renzi has accomplished an important task and is regarded with great esteem by Obama Ambassador John Phillips

Speaking at a meeting on transatlantic relations in Rome, he said: “The referendum is an Italian decision but Italy must ensure political stability. 63 governments in 63 years gives no guarantee.” Mr Phillips insisted the referendum “"offers hope on government stability to attract investors” as the debt-ridden country faces collapse. In a boost to US-Italy relations, Mr Phillips said: "Renzi has accomplished an important task and is regarded with great esteem by Obama, who appreciates his leadership."

But as violent riots break out in Naples and Sicily and Mr Renzi threatens to resign if he loses the November vote, Italian politicians have criticised the ambassador’s comments. Matteo Salvini, leader of the Lega Nord party, said: “Mr Ambassador, mind your own business and don’t interfere as too often has happened in the past, in Italian internal affairs. “I hope Trump wins in November. He has said he will deal with his own issues.”

GETTY US ambassador to Italy John Phillips warned saying no to the referendum would be a step backwards

REUTERS Italian Prime Minister Matteo Renzi gave the go ahead for the vote on constitutional reform

Movimento Sociale Italiano member Maurizio Gasparri branded Mr Phillips’ comments an "unacceptable interference" and demanded an apology. It’s not the first time the US has waded into another country’s referendum. President Barack Obama sparked outrage when he said “Britain will be at the back of a queue” when it comes to trade deals if the nation voted for Brexit. The under-fire Mr Renzi is due to travel to Washington next month to attend a state dinner hosted by President Obama.

EPA Violence has erupted in Naples ahead of the vote

EPA Protests have broken out across Italy as Mr Renzi comes under fire

Having pegged his political future on the referendum Mr Renzi called up President Obama's former political advisor Jim Messina for advice on how to win the vote. Mr Messina, who led President Obama's successful 2012 re-election campaign, met Mr Renzi's inner circle in late July to discuss what they should do to regain the initiative after opinion polls showed the Italian leader faced defeat. EU allies are awaiting the referendum, with alarm, fearing a 'No' vote could revive political instability in the eurozone's third largest economy.

One former EU official, who asked not to be named, said: "The biggest worry I have is Italy. If Renzi loses the referendum then the eurozone is in trouble. Without Renzi we are in no man's land." Buoyed by positive opinion polls, Mr Renzi promised last year to resign if he lost the referendum on his flagship reform, which will shrink the Senate, the upper house of parliament, and strip it of the power to bring down governments. The Prime Minister, who came to power in 2014 following an internal party coup, says this will bring political stability to Italy, which has had 63 governments since the Second World War.

Brexit aftershocks: Who's next to leave the EU? Wed, September 14, 2016 Britain has voted to leave the EU. So who's next? We look at which European countries want to hold their own EU referendum. Play slideshow Express 1 of 10 Frexit, Nexit or Auxit? Who will be next to leave the EU