(NBC News) - Former Secretary of State Colin Powell blasted Donald Trump as a "national disgrace" and "international pariah" in a personal email exchange that was leaked online by hackers.

Powell, a retired 4-star general and a Republican, confirmed the authenticity of the emails to NBC News.

"The hackers have a lot more," he added.

The contents of the emails were first reported by Buzzfeed News. It said the messages had been obtained by the website which MSNBC reported is rumored to have ties to Russian intelligence services.

Powell called Trump a "national disgrace" and "international pariah" in a June 17 email to a former aide, saying the Republican presidential contender was "in the process of destroying himself, no need for Dems to attack him."

A subsequent email to the same former aide on Aug. 21 slammed Trump for spurring the "racist" so-called "birther" movement — the consistently debunked rumor that President Barack Obama was born in another country.

"Yup, the whole birther movement was racist," Powell wrote, according to Buzzfeed. "That's what the 99% believe. When Trump couldn't keep that up he said he also wanted to see if the certificate noted that he was a Muslim."

There was no immediate response from the Trump campaign to the emails.

The revelations mark the latest in a string of headlines around Powell's email correspondence. His online activity has figured heavily of late into the controversy around Hillary Clinton's use of a private email server.

Powell expressed frustration about his name being linked to Clinton's email issues, writing in another leaked email: "I have told Hilleary's [sic] minions repeatedly that they are making a mistake trying to drag me in, yet they still try," Powell wrote.

While Powell has described himself as a lifelong Republican, he twice endorsed Obama — a Democrat — for president.