Scuffles have broken out at a rally in Arizona - after billionaire Donald Trump launched another attack on Mexican immigrants.

He is trying to drum up support for his bid to secure the Republican nomination for the American presidency next year.

He told the crowd in Phoenix that "I respect Mexico greatly as a country, but the problem we have is that their leaders are much smarter, sharper, and more cunning than our leaders, and they're killing us at the border and they're killing us in trade."

There were brief scuffles between supporters of Trump and protesters during what Time called a 'rambling speech'.

At a separate event in Las Vegas, Mr Trump said immigrants "wreak havoc on our population."

Last month, Mr Trump caused outrage by suggesting many Mexicans migrating to the States were drug runners and rapists.

Colleen Graffy used to be a senior US government official, and says some of the things Donald Trump is saying about immigration are resonating:

Trump's previous comments have seen several lucrative business deals he has previously made fall through, with numerous business partners, including the NBC television network, sever ties with the controversial would-be politician.

Last month, Mr Trump announced he will run for the US presidency, confirming earlier speculation.

Trump - who is a Republican - told Newstalk Breakfast during an interview that "we're going to have a wild time, because the United States should be doing much better than it's doing".