David Jackson

USA TODAY

After more than a month of speculation, President-elect Donald Trump has selected ExxonMobil CEO Rex Tillerson as his secretary of State nominee and will make the announcement on Tuesday.

A person familiar with the selection confirmed, speaking on condition of anonymity pending Trump's announcement.

"I will be making my announcement on the next Secretary of State tomorrow morning," Trump tweeted Monday night.

Democrats and some Republicans have raised questions about Tillerson's business ties to Russia, though Trump has described the 64-year-old oil industry executive as a major player on the world stage.

Trump told Fox News Sunday that Tillerson is "much more than a business executive."

"I mean, he's a world-class player," said Trump. "He's in charge of, I guess the largest company in the world. He's in charge of an oil company that's pretty much double the size of his next serious competitor. "

Trump also told Fox that "a great advantage is he knows many of the players, and he knows them well. He does massive deals in Russia. He does massive deals for the company — not for himself — for the company."

The president-elect tweeted on Sunday, amid reports he planned to pick Tillerson, that "whether I choose him or not" the Exxon executive "is a world class player and dealmaker. Stay tuned!"

The 2012 Republican presidential candidate Mitt Romney had previously been considered as a favorite for the Cabinet slot, but in a Facebook post on Monday Romney made it clear that he was out of the running. Romney was heavily criticized by Trump loyalists for his attacks on Trump during the campaign.

"It was an honor to have been considered for Secretary of State of our great country," Romney wrote. "My discussions with President-elect Trump have been both enjoyable and enlightening. I have very high hopes that the new administration will lead the nation to greater strength, prosperity and peace."

Concerns about Tillerson's connections to Russia come amid reports that Vladimir Putin's government may have intervened in the U.S. presidential election in an effort to steer the result in Trump's favor. Putin and Trump have both dismissed the allegations.

Exxon's $2.2 billion investment in Russian oil exploration in the Artic Ocean will likely be a source of discussion in Tillerson's Senate confirmation hearing. The agreement, negotiated by Tillerson, was eventually killed by U.S. sanctions against Russia after the annexation of Crimea.

“I have obviously concerns of reports of his relationship with Vladimir Putin, who is a thug and a murderer," Sen. John McCain, R-Ariz., told CNN.

Among the people previously considered contenders to serve as Trump's top diplomat were Romney, ex-New York City Mayor Rudy Giuliani (who withdrew his name from consideration on Friday), Senate Foreign Relations Committee chairman Bob Corker, and retired general and ex-CIA director David Petraeus.