US Democratic presidential candidate Hillary Clinton has lambasted Donald Trump's foreign policy platform as "dangerously incoherent", casting her Republican rival as both a dangerous and laughable figure.
The former US secretary of state attacked Mr Trump for his policies and character, suggesting he might start a nuclear war if elected to the White House simply because "someone got under his very thin skin".
"Donald Trump's ideas are not just different, they are dangerously incoherent," she said to a room of supporters in California.
"They're not even really ideas, just a series of bizarre rants, personal feuds and outright lies."
Ms Clinton, the front-runner in the race to become the Democratic presidential nominee, delivered her speech as she shifts her attention to the November election against likely rival Mr Trump and away from Bernie Sanders, a Vermont senator, who is continuing his longshot bid for the nomination.
Mr Trump, the Republicans' presumptive nominee, says he would sit down with North Korean leader Kim Jong Un to try to stop Pyongyang's nuclear program and has criticised the decades-old NATO alliance with mainly European nations as obsolete and too costly for the United States.
The billionaire businessman, who has never held elected office or worked in government before, says he has experience dealing with foreign governments through setting up hotels, resorts, golf courses and beauty pageants in foreign countries.
Ms Clinton, who is also a former US senator and first lady, mocked this.
Mr Trump has talked tough on foreign policy.
He wants to bring back waterboarding and other brutal interrogation techniques for terrorism suspects that are widely regarded as torture and were discontinued by President Barack Obama.
He has also vowed to renegotiate trade deals, called for a temporary ban on Muslims entering the country, and said he would ask members of the 28-nation NATO alliance to "pay up" or "get out".
Mr Trump has criticised Ms Clinton for her handling of foreign policy during her 2009-2013 stint as foreign secretary, including the September 11, 2012, attack by Islamist militants on a US diplomatic facility in Benghazi, Libya, that killed the US ambassador and three other Americans.
He cites Ms Clinton's support for the Iraq war -- launched by former Republican President George W Bush -- as another example of her shortcomings.
At a rally Wednesday night in Sacramento, California, Mr Trump said he had seen a copy of Ms Clinton's speech and "it was such lies about my foreign policy".