Iowa caucus: Cruz leads Trump in Republican opinion poll
A survey asking Republican supporters in the key US state of Iowa to pick a presidential candidate has placed Texas Senator Ted Cruz ahead of Donald Trump, who leads in most national polls.
The poll, ordered by Bloomberg Politics and The Des Moines Register, gave Mr Cruz a 10-point lead over Mr Trump.
Iowa helps shape the race to the White House by being the first state to hold a caucus deciding each party's nominee.
The latest survey suggests a higher chance of a bitter, protracted primary.
According to the New York Times, the arch-conservative Mr Cruz could emerge as the preferred nominee of far-right Republicans, competing against Mr Trump - cast as an anti-establishment candidate - and against a possible third candidate representing the centre-right of the party.
Both Mr Cruz and Mr Trump have been campaigning heavily in Iowa, and hope victory in the 1 February caucus will galvanise their race for the Republican nomination.
In the poll, 31% of respondents wanted Mr Cruz to secure the nomination, compared with 21% naming Mr Trump as their first choice.
Mr Trump attacked The Des Moines Register's credibility before the poll was released, describing the paper as "dishonest" and singling out its lead political reporter as "the worst".
Mr Trump and Mr Cruz have also been trading barbs in recorded statements and on Twitter, prompting speculation that an unofficial pact between the two men has unravelled.
The relationship between the two candidates was until recently thought to be cordial, based on remarks they had made about each other to the press.
There was more good news for the Texas senator in an NBC News/Wall Street Journal national poll, which had him surging into second place behind Mr Trump, with Ben Carson dropping 18 points to fourth place.
Trump's candidacy - in depth
Could Trump really be US president? - five experts give their views
Video: 'It was just a movie' - Harrison Ford tells Trump presidency is not like films
Trump's die-hard supporters - Who are the thousands of people standing behind their man, through thick and thin?
Party problem? - Is Trump destroying the Republican party?
'UK politicians should be thanking me' - Trump hits back at high-profile Scottish snubs
Mr Trump remains the most popular Republican candidate according to most national polls.
The billionaire businessman and TV star was heavily criticised by other candidates for proposing a ban on Muslims entering the US on the grounds that they may pose a security threat.
The next Republican debate is on Tuesday.
Hillary Clinton is the favourite to win the Democratic nomination for the presidential election, which will be held in November next year.