Ted Cruz, the firebrand Texas senator, has won Iowa’s Republican caucus, as Hillary Clinton and Bernie Sanders remained neck-and-neck in the Democratic race with only a few precincts left to count.

Mr Cruz’s victory represents a blow to Donald Trump, the New York property mogul who had dominated the GOP race for months. With 99 per cent of precincts reporting in the first state to vote in the 2016 presidential race, Mr Cruz had won 28 per cent compared to Mr Trump’s 24 per cent.

In another setback for the billionaire’s anti-establishment campaign, Marco Rubio, the Cuban-American senator favoured by establishment Republicans, won 23 per cent - an upset for pollsters who mostly forecast a Trump victory and had not predicted the strength of Mr Rubio’s support.