Ted Cruz has caused a big upset by beating Donald Trump in the Republican Iowa caucuses, while Hillary Clinton claimed an extremely narrow victory over rival Bernie Sanders in the Democrats' race.
The caucus is the first vote in the race for the US presidential nominations for both parties, and is seen as an important bellwether for candidates' chances in the elections.
Hillary Clinton's campaign has declared victory over Bernie Sanders in the Iowa caucus.
In a statement, the official Clinton campaign said there was "no uncertainty" that Hillary Clinton had won the nominating contest.
The Democrat rivals were deadlocked with both receiving roughly 50% of the vote in what Bernie Sanders previously declared as a "virtual tie."
Bernie Sanders' brother says he thinks his sibling has what it takes to win the next US Presidency.
There is much still to play for in both parties in the first real test for America's would-be presidents.
Ted Cruz caused a huge upset by beating Donald Trump in Iowa's Republican caucuses.