Cruz told the 2,000 delegates at the Quicken Loans Arena on Wednesday evening that Americans must "vote with [their] conscience" in November. Delegates on the floor urged Cruz to endorse the nominee, chanting Trump's name.

Trump - who will represent the party in the November 8 election against the presumptive Democratic nominee Hillary Clinton - entered the hall near the end of Cruz's speech.

Cruz, who finished second to Trump in a very bitter Republican primary campaign, mentioned Trump once in his speech and did not say he would vote for the New York billionaire.

"We deserve leaders who stand for principle, who unite us all behind shared values, who cast aside anger for love. That is the standard we should expect, from everybody," he said, to both cheers and boos from the crowd.

"Stand, and speak, and vote your conscience, vote for candidates up and down the ticket who you trust to defend our freedom and to be faithful to the Constitution."

Trump responded on Twitter, refering to a promise they had both made during the primaries to endorse whoever became the Republican presidential nominee.

#Tweet:755972015249645568#

A poor reception

The decision to accept a speaking role at the convention but not endorse Trump went down very badly among rank and file Republicans in Cleveland, with reported angry scenes unfolding after the speech between Cruz and Trump supporters.

Cruz had been very critical of Trump in the last weeks of their primary battle earlier this year, calling the businessman a "pathological liar" and "utterly amoral."

The booing was so intense that the Trump campaign reportedly encouraged its staffers on the convention floor to try to calm the delegates down. Interrupted by chants of "Trump, Trump, Trump," Cruz said with a smile, "I appreciate the enthusiasm of the New York delegation."

A Cruz backer and former Virginia Attorney General Ken Cuccinelli escorted Heidi Cruz off the convention floor as she was heckled by delegates.

Trump's family and friends in attendance turned their backs on Cruz to stand and applaud the Republican nominee, who sat down in the front row of his VIP box to watch his son Eric deliver the next speech.

Despite party elder Newt Gingrich's subsequent attempt to spin Cruz's apparent snub as an implicit endorsement of Trump, the Texas senator appeared content to talk generalities, outlining the conservative principles he believes underpin the party and urging voters not to stay home without voting in November's presidential election.

jbh/gsw (dpa, AP)