Donald Trump endorsed by former US VP nominee Sarah Palin

Republican presidential candidate Donald Trump has received the "coveted" endorsement from former Republican vice-presidential candidate Sarah Palin.

Palin, who was named by John McCain as an ultimately unsuccessful running mate during the 2008 campaign, praised the billionaire's leadership and "unparalleled ability to speak the truth and produce real results", she said at a Trump rally at Iowa State university.

ITV News Washington correspondent Robert Moore reports:

"Media heads are spinning," Ms Palin said after taking the stage.

"This is going to be so much fun."

In a somewhat rambling speech, she said that, with Mr Trump as president, America would no longer apologise.

"No more pussy-footing around," she said, adding that Mr Trump would allow the military do its job and destroy the Islamic State group.

At one point, Ms Palin appeared to call for a future US president to put domestic policy first, and bizarrely urged Middle Eastern "oil-rich" countries to "duke it out" and let "Allah sort it out" - perhaps a reference to the ongoing threat from the so-called Islamic State in Libya, Syria and Iraq.

In response, Trump said he was greatly honoured to receive the support from a "trusted conservative".

Earlier on Tuesday, Mr Trump received an endorsement from the daughter of Hollywood star John Wayne.

Standing in front of a life-size, rifle-toting model of the actor in full cowboy gear, Mr Trump accepted the endorsement of Aissa Wayne at the John Wayne Birthplace Museum in Winterset, Iowa.

"America needs help and we need a strong leader and we need someone like Mr Trump with leadership qualities, someone with courage, someone that's strong, like John Wayne," she said.

But the rest of the Wayne family and its interests were quick to distance themselves from Mr Trump.

John Wayne Enterprises president Ethan Wayne, a son of the actor, said in a terse statement: