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ExxonMobil CEO and chairman Rex Tillerson. Image courtesy of ExxonMobil.

President-elect Donald Trump has officially nominated ExxonMobil CEO Rex Tillerson to lead the U.S. State Department.

In a Twitter message posted early Tuesday morning, Trump said he has chosen “one of the truly great business leaders of the world, Rex Tillerson, Chairman and CEO of ExxonMobil, to be Secretary of State.”

In a followup post, Trump added “the thing I like best about Rex Tillerson is that he has vast experience at dealing successfully with all types of foreign governments.”

Tillerson, 64, has not commented on the matter.

Tillerson has spent his entire career at ExxonMobil, joining the company in 1975 after graduating from the University of Texas at Austin.

Tillerson was slated to retire next year after turning 65, Exxon’s mandatory retirement age.

Tillerson emerged as a front-runner for the post after former New York mayor Rudolph Giuliani withdrew his name from consideration last week.

Tillerson’s business ties to Russia’s Rosneft have become a point of interest for Congressional members who must approve his nomination.

During Tillerson’s tenure, Exxon partnered with Rosneft to explore offshore Arctic plays.

Exxon was forced to wind down its $600 million Kara Sea project in late 2014 after U.S. sanctions were tightened after Russia annexed Crimea.

ExxonMobil is partnered with Rosneft at the Universitetskaya-1 license where the Kara Sea project is located.

Tillerson was awarded the Order of Friendship by Russian President Vladimir Putin in 2013, about two years after Exxon signed a strategic cooperation deal with Rosneft.

Tillerson’s views on U.S. sanctions against Russia have also drawn scrutiny.

During Exxon’s 2014 shareholders meeting, Tillerson said Exxon “does not support sanctions” and believes that sanctions are usually “not effective.”

According to a transcript seen by NBC News, Tillerson added during the meeting that sanctions are effective only when they are ” implemented comprehensively” and added that implementing sanctions is a “very hard thing to do.”

The nomination is likely to receive push back from Congressional members, some of whom have expressed concern about Tillerson’s relationship with Putin.

In a series of Twitter messages posted on Tuesday, Senator Lindsey Graham said that there are “many questions” to be answered about Tillerson’s “extensive business dealings with the Putin government & previous opposition of efforts to impose sanctions on the Russian government.”

Senator John McCain told CBS News on Sunday that Tillerson’s “close personal relationship” with Putin is a matter of “concern.”

Senator Marco Rubio said on Twitter that “being a friend of Vladimir is not an attribute I am hoping for from a .”

The American Petroleum Institute applauded Tillerson’s nomination on Tuesday, calling him a “world class” choice.

“As our nation’s next top diplomat, Rex has the strategic experience to effectively represent the new administration and the American people,” API President and CEO Jack Gerard said in a statement.