Republican Ted Cruz and Democrat Bernie Sanders win victories in Wisconsin
Republican Ted Cruz has won the Wisconsin presidential primary in a blow to rival Donald Trump.
The win is a breakthrough for those in the Republican Party battling to block Mr Trump who has so far been the front runner in the contest.
It also raises the prospect of a prolonged nominating fight that could last up to the party convention in July.
"We've got the full spectrum of the Republican party coming together and uniting behind this campaign," Cruz told a Wisconsin rally.
Mr Trump had 737 convention delegates to Cruz's 481 heading into the Wisconsin vote, leaving him 500 delegates short of the 1,237 needed to win nomination going into the US election.
The Wisconsin primary followed a difficult week for Mr Trump, after he had to backtrack over his comments that women who have abortions should face punishment if the procedure is outlawed.
Mr Cruz and Ohio Governor John Kasich, the other remaining Republican contender, hope to stop Mr Trump short of a first-ballot victory and trigger a contested convention.
Also in Wisconsin, there was a win for Democratic presidential contender Bernie Sanders, further cutting into the lead of front-runner Hillary Clinton.
The win was the Vermont senator's sixth in the last seven nominating contests.
"What we have been seeing throughout this campaign is extraordinary voter turnout in state after state," Mr Sanders said at a rally in Laramie, Wyoming.
Ms Clinton, who did not appear in public on Tuesday night, tweeted her congratulations to her rival.
She may be able to afford to be generous as Mr Sanders needs to win up to two-thirds of the remaining delegates to catch up with her.