US Senator Ted Cruz beat billionaire Donald Trump in Iowa's Republican presidential nominating contest on 1 February, upsetting the national front runner in the race to be their party's White House nominee.

"Tonight is a victory for the grass roots. Tonight is a victory for courageous conservatives across Iowa and all across this great nation. Tonight the state of Iowa has spoken," Cruz told his supporters after the votes were tallied.

Cruz, a conservative lawmaker from Texas, won with 28% of the vote compared to 24% for businessman Trump. Marco Rubio, a US senator from Florida, came in third place with 23%.

"The last seven years of having a president, having an attorney general, that demonises you, that vilifies you, that sides with the criminals and looters instead of the brave men and women of law enforcement – that will end on 20 January 2017," Cruz said.

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"The Democrats here seem to be in a virtual tie between one candidate who admits he's a socialist and the other candidate who pretends she's not," Cruz said.

"The problem with socialism is eventually you run out of other people's money," Cruz said paraphrasing former British prime minister Margaret Thatcher.

Clinton, a former secretary of state, and Bernie Sanders, a self-described democratic socialist US senator from Vermont, both came in at roughly 50% with 95% of the state's precincts reporting results. Sanders declared the results a tie.