Donald Trump's presidential campaign said it has fired top political adviser Roger Stone, CBS News has confirmed.

"Mr. Trump fired Roger Stone last night," a campaign spokesperson told CBS News Saturday. "We have a tremendously successful campaign, and Roger wanted to use the campaign for his own personal publicity."

Trump's campaign took issue with Stone and "a number of articles about him recently," saying that the business mogul "wants to keep the focus of the campaign on how to Make America Great Again." The news was first reported by the Washington Post.

But Stone, a longtime Trump aide and a former Richard Nixon associate, denied that he had been fired.

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"I resigned this morning -- categorically deny being fired," Stone told CBS News in an email.

In another interview with CBS News, Stone added that he resigned for "constructive reasons."

"We don't have time for political correctness," Stone told CBS News correspondent Julianna Goldman. "But the campaign seems to have run into a cul-de-sac and I'm disappointed by the lack of specificity put forward by the campaign today."

Stone contended that the campaign "has gotten seriously off message" and relied on "unscientific polls" with "no value."

Responding to the campaign's allegations that Stone was a personal publicity seeker, the former aide called the comments "ludicrous." Still, Stone said he did not regret "in any way, shape, or form" being associated with the billionaire's presidential run.

A longtime friend of Stone also told CBS News that Stone "reached out to me last night and early this morning about his intentions and it was to quit." Another source with firsthand knowledge of the decision told CBS News that "he resigned first."

The New York Times' Maggie Haberman reported on Twitter that Stone actually sent a resignation letter to the Trump campaign early Saturday morning:

Stone denies being fired - sent letter resigning this mornning. — Maggie Haberman (@maggieNYT) August 8, 2015

Stone criticized the campaign in the resignation letter, which CBS News has obtained a copy of, saying "the current current controversies involving personalities and provocative media fights have reached such a high volume that it has distracted attention from your platform and overwhelmed your core message."

Stone added that he was "proud of to have played a role in the launch" of Trump's presidential campaign," and that he still cared about the business mogul "as a friend."

"We have enjoyed a close relationship - both personal and political/professional - since the 1980s. You know that I wish only the best for you," Stone penned in the letter.

But "[w]ith this current direction of the candidacy," Stone wrote, "I no longer can remain involved in your campaign."

Stone, who began his political career in college working on Nixon's Committee to Re-Elect the President and has since worked for Ronald Reagan and Bob Dole, used to head Trump's casino lobbying efforts in Washington. He's widely known in Republican circles as a "dirty trickster," a moniker given by the New Yorker in a wide-ranging 2008 profile of Stone.

According to a source close to Stone, while working for Trump, the former lobbyist felt marginalized as the only Trump adviser with "extensive presidential campaign experience." Stone reportedly felt that other aides had egged on Trump's feud with Megan Kelly, saying that online polls like Drudge showed Trump gaining from his attacks on his critics.

Trump, in the latest contentious episode of a campaign fraught with controversy, recently came under fire for comments he made after Thursday's first GOP debate. Trump attacked Fox News moderator Megyn Kelly for her questions on how he treated women, insinuating that she was angry and hormonal during the debate.

"There was blood coming out of her eyes, blood coming out of her wherever," Trump told CNN Friday.

CBS News' Sopan Deb and Steve Chaggaris contributed to this report.