Hillary Clinton has warned her Republican presidential rival Donald Trump about his "casual inciting" of violence, saying his remarks suggesting gun rights supporters could act against her "crossed the line."
"Yesterday we witnessed the latest in a long line of casual comments by Donald Trump that crossed the line," Mrs Clinton, the Democratic nominee, told supporters in Des Moines, Iowa.
She said: "Words matter, my friends. And if you are running to be president, or you are president of the United States, words can have tremendous consequences."
Mr Trump's remarks on Tuesday caused huge controversy, including among some Republicans, when he suggested that "Second Amendment people" - those who support gun rights - could take action to stop Mrs Clinton from appointing US Supreme Court justices as president.
He and his campaign quickly sought to defuse the situation, insisting the businessman was merely urging gun rights supporters to reject her candidacy at the ballot box.
Mrs Clinton appeared to reject the Trump campaign's defence, warning of the dangers of reckless language during a presidential race.
She criticised Mr Trump's "casual cruelty to a gold star family," referring to the billionaire's clash with the parents of a Muslim American soldier who was killed in action.
"His casual suggestion that more countries should have nuclear weapons, and now his casual inciting of violence," she added.
"Every single one of these incidents shows us that Donald Trump simply does not have the temperament to be president and commander in chief of the United States."
Moments before Mrs Clinton's remarks, a man later described by US media as an animal rights activist appeared to try to force his way on stage, but was stopped and removed by US Secret Service agents.
Agents rushed onto the stage to protect the candidate, but retreated after the protester was escorted out.
