Ted Cruz caused a huge upset by beating Donald Trump in Iowa's Republican caucuses.

Cruz won 28% of the vote, finishing ahead of Trump - who has led the polls for weeks - and Marco Rubio.

Votes are still being counted in the Democratic contest, but Hillary Clinton said she was "breathing a big sigh of relief" while the self-styled Democratic socialist Bernie Sanders said they were in a "virtual tie".

The Texas senator declared his win as a "victory for courageous conservatives" as he criticised the media, Washington establishment and lobbyists.

"Iowa has sent notice that the republican nominee and the next president of the United States will not be chosen by the media, will not be chosen by the Washington establishment," the 45-year-old told cheering supporters.

The result was reward for Cruz's relentless campaigning in the state, where he was sought to win the Conservative and evangelical vote.

Trump said he congratulated Ted Cruz on his victory and said he was "honoured" to finish second.

But the billionaire - who has dominated the polls and the headlines for weeks - said he still expected to win the Republican nomination for the November 8 election.

He vowed to "easily beat Hillary or Bernie or whoever the hell they throw up there".

But this result - along with a strong showing from Rubio - could halt Trump's once seemingly unstoppable momentum, which has alarmed the Republican establishment.

Hillary Clinton and Bernie Sanders appear to be deadlocked in an increasingly fascinating battle to be the Democratic choice for the White House.

Clinton admitted she was "breathing a big sigh of relief" but stopped short of claiming victory as she spoke to supporters afterwards.

Mr Sanders, 74, said "it looks like we are in a virtual tie".

He also said he was overwhelmed by his surge in support which has taken commentators - who believed Clinton was assured of victory - by surprise.

"We had no money, we had no name recognition, and we were taking on the most powerful political organisation in America," the Vermont senator told his jubilant supporters.

Martin O'Malley, who failed to keep up with Hillary Clinton and Bernie Sanders, withdrew from the race to be the Democratic candidate after a dismal showing in Iowa.

Mike Huckabee tweeted that he was also going to suspend his campaign to be the Republican nominee.

Ben Carson was also forced to deny rumours he was about to withdraw after it emerged that he was planning on returning to Florida after the vote instead of travelling to New Hampshire for next week's contest.

ITV News Washington Correspondent Robert Moore writes:

Read more of Robert's analysis of the Iowa caucuses.