President-elect Donald Trump nominated Exxon Mobil CEO Rex Tillerson Tuesday to be secretary of state after weeks of speculation over who would fill the job, but it quickly became clear some Republicans aren't comfortable with his choice.

Rice and Gates, who have worked for Exxon as consultants, both issued statements of support on Tuesday.

Senator Marco Rubio, who lost to Mr Trump in the Republican primaries, said he had serious concerns about the nomination.

"He will be a forceful and clear-eyed advocate for America's vital national interests, and help reverse years of misguided foreign policies and actions that have weakened America's security and standing in the world".

Tillerson's "cozy ties to Vladimir Putin and Russian Federation would represent an untenable conflict at the State Department", Representative Eliot Engel, the ranking Democrat on the House of Representatives Committee on Foreign Affairs, said in a statement.

With 10 Republicans and nine Democrats sitting in the Senate Foreign Relations Committee, it would take only one Republican defection to block the appointment.

In 2013, Vladimir Putin presented the Texan with the Order of Friendship, one of the highest honors a foreigner may be awarded from Russian Federation.

"It ironically continues something that really started in the Clinton State Department which is economic statecraft and the fact that U.S. CEOs, U.S. companies have been some of our best diplomats overseas and the U.S. brand is an important part of U.S. diplomacy and U.S. representation", Mortlock said.

In comments to Tillerson's possible nomination, Kremlin spokesman Dmitry Peskov said on December 12 that he expects that the new USA secretary of state will show professionalism and a constructive attitude, regardless of who will hold office. "Mr. Tillerson's experience with Russia and the Russian president will prove to be invaluable". John McCain of Arizona recently described Putin as a "thug, bully, and a murderer" and said he anxious that Tillerson's "enormous deals" with Russia "would color his approach to Vladimir Putin and the Russian threat".

The Tillerson nomination comes amid news reports that the Central Intelligence Agency believes the Russians interfered in the election by hacking Democratic officials' e-mail accounts, seeking to discredit Democratic candidate Hillary Clinton and promote Trump's chances.

Over the weekend, McCain said on "Face the Nation" that Tillerson would get a fair Senate hearing but that he had reservations about him being the nominee. "We'll have some questions".

"I look forward to meeting Mr. Tillerson and discussing his world view - especially his views of the U.S".

The CIA recently concluded with "high confidence" that Russian Federation sought to influence the U.S. election on behalf of Trump, raising red flags among lawmakers concerned about the sanctity of the USA voting system and potentially straining relations at the start of Trump's administration.

While not denouncing the Tillerson nomination, Sen. "Through hard work, dedication and smart deal making, Rex rose through the ranks to become CEO of ExxonMobil, one of the world's largest and most respected companies", the billionaire real estate mogul said in a predawn news release from Trump Tower in NY.

The Senate Foreign Relations Committee is scheduled to hold a hearing on the nomination in early January.