Ted Cruz was booed by furious delegates for refusing to endorse Donald Trump, undermining calls for Republican unity.

The remarkable scenes overshadowed the speech by Indiana Governor Mike Pence, who was formally nominated for vice-president.

Mr Cruz, a Texas senator, was defeated by Mr Trump in the race to become Republican candidate in the race for the White House, and spoke on the third day of the party's convention in Cleveland, Ohio.

He mentioned Mr Trump by name only once, and stubbornly refused to endorse him, triggering thunderous boos from angry delegates as he encouraged Americans to simply "vote your conscience" in November.

Mr Trump - who will address the fourth and final day of the conference - unexpectedly walked into the arena just as Mr Cruz was ending his remarks.

Delegates chanted Mr Trump's name and implored Mr Cruz to voice his support for the businessman, to no avail.

Mr Cruz's wife Heidi had to be escorted from the convention floor for her own safety as she was heckled by Trump delegates.

The extraordinary scenes show how split Republicans are following Mr Trump's controversial campaign, and were at odds with the later claim by Mr Pence that it was a "united party".