Supporters and opponents of Republican presidential nominee Donald Trump have clashed in the city of San Diego, California.
Some protesters threw stones and water bottles at each other outside the San Diego Convention Center. Police said 12 people were arrested.
Mr Trump was in the city near the Mexican border to hold a rally ahead of the 7 June California primary.
He has pledged to build a border wall to keep out illegal immigrants.
Police in riot gear were deployed in San Diego to keep the rival camps apart.
"I am opposed to the hateful, bigoted, racist language of Donald Trump and his arrogance and intolerance," San Diego protester Martha McPhail told the local City News Service.
"I'm for all of our people - all races, sexes, genders, military veterans - and he's divisive," she added.
Trump supporter Riley Hansen defended the controversial businessman.
"My Dad always told me you need a businessman as president. I like his policies," he told CNS.
Image copyright AFPEarlier on Friday, Mr Trump backed out of an offer to debate with Democratic candidate Bernie Sanders.
"As much as I want to debate Bernie Sanders - and it would be an easy payday - I will wait to debate the first place finisher in the Democratic Party, probably Crooked Hillary Clinton, or whoever it may be," the Trump campaign said in a statement.
Mr Sanders told reporters on the campaign trail that he hoped Mr Trump would change his mind.
"Well Mr Trump, what are you afraid of?" he said, calling the Republican nominee a "bully".
Mr Trump said the Democratic nominating process was "rigged" - and that Mrs Clinton and Democratic National Committee Chairwoman Deborah Wasserman Schultz would not allow Mr Sanders to win the nomination.