Leaked emails from former Secretary of State Colin Powell showed him strongly criticising Republican presidential candidate Donald Trump, labelling him a "national disgrace and an international pariah".
"He appeals to the worst angels of the Republican nature and poor white folks," CNN on Thursday quoted Powell as saying in an August email.
Powell, also a Republican, called the birther movement (President Barack Obama's citizenship conspiracy theory), which Trump helped lead, "racist".
"That's what the 99 per cent believe. When Trump couldn't keep that up he said he also wanted to see if the certificate noted that he was a Muslim," Powell wrote.
The messages, the existence of which were first reported by BuzzFeed and The Intercept, were posted to DCleaks, an organisation affiliated with other recent hacks of high-profile figures.
Peggy Cifrino, an aide to Powell, told CNN "The emails are accurate. No further comment at this time."
Powell also mocked Trump's proposal that he could win over the African-American population.
"For him to say that within four years he would have 95 per cent of blacks voting for him is schizo fantasy," Powell wrote.
The mails also showed Powell angry with Democratic presidential candidate Hillary Clinton over her handling of her personal emails as secretary of state.
Powell wrote in 2015, "Everything HRC (Hillary Rodham Clinton) touches she kind of screws up with hubris."
The FBI released information from its investigation of Clinton's email practices in July and August, and the notes it released showed Clinton indicating her practices came from Powell, CNN added.