President-elect Donald Trump (left) and Vice President-elect Mike Pence (right) greet retired Marine General James Mattis in Bedminster, New Jersey, Nov. 19, 2016. Reuters

Retired Marine Gen. James Mattis, colloquially known as "Mad Dog," has been chosen by President-elect Donald Trump to serve as secretary of defense in his cabinet, the Washington Post reported Thursday. But Trump's team quickly pushed back against the report saying nothing was official yet.

The Post cited "people familiar with the decision" but also reported neither Mattis nor representatives for the Trump transition team would confirm the choice. CNN later confirmed the Washington Post report, citing a source with knowledge of the transition team. An official announcement was likely to come early next week, according to the reports.

Shortly after the articles published, however, Jason Miller, Trump's communications director, tweeted that no decision had been made on the secretary of defense post. He also pushed back on the news in an interview with the conservative news outlet Washington Examiner, saying, "My sources are better than their sources. Trust me on that one."

Mattis was celebrated for his service during the war in Iraq, especially in the battle of Fallujah in 2004. In total, he served for some 40 years in the military and eventually took over as the head of U.S. Central Command in July 2010. He had disagreements with a number of President Barack Obama's policies, however, and has said American influence has weakened significantly in the Middle East. Mattis retired in 2013.

The former general is widely respected, especially among conservatives, and has a reputation for speaking bluntly. He's been quoted as saying both "be polite, be professional, but have a plan to kill everybody you meet," as well as, "engage your brain before you engage your weapon."

If Mattis were the secretary of defense choice, Congress would need to make an exception for him to bypass a rule that says defense secretaries aren't allowed to have been on active duty within seven years of their nomination.

While the running for defense secretary could be over, Trump has apparently expanded his list of candidates for secretary of state.

MSNBC's Joe Scarborough tweeted Thursday that Exxon Mobil Corporation CEO Rex Tillerson had been added to the mix. Tillerson has no government experience.

Scarborough also tweeted that former GOP presidential nominee Mitt Romney, with whom Trump had dinner recently, would have already been named secretary of state if there had not been "blowback." Many people loyal to Trump reportedly felt Romney shouldn't be chosen because he's a Republican establishment figure who had railed against the president-elect during the campaign.