US President-elect Donald Trump has officially announced he will to nominate ExxonMobil CEO Rex Tillerson as Secretary of State.

Mr Trump praised the 64-year-old Republican as one of the world's most successful businessmen.

"Rex Tillerson's career is the embodiment of the American dream. 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," Mr Trump said.

As secretary of state, Mr Tillerson says he will focus on strengthening alliances, while pursuing "shared national interests and enhancing the strength, security and sovereignty of the United States."

As ExxonMobil's president and CEO, the 64-year-old Texan oversees the company's business activities in more than 50 countries.

He has opposed sanctions on Russia and in 2013 was awarded Russia's Order of Friendship by President Vladimir Putin following several years of Exxon projects in the country.

The nomination needs Senate approval.

US media have been reporting for days on secret CIA findings that Moscow sought to bolster Trump's election bid against former secretary of state Hillary Clinton by releasing hacked Democratic Party documents.

Tillerson -- who has no formal foreign policy background -- is sure to face sharp questions in the Senate confirmation hearings.

Senior Republican Senator John McCain has said Tillerson's ties to Putin are "a matter of concern."

"Vladimir Putin is a thug, bully and a murderer, and anybody else who describes him as anything else is lying," McCain said before the nomination was formalized.

Democratic congressman Eliot Engel, the top Democrat on the House Foreign Affairs Committe, said Tillerson was "not qualified."

"Aside from his utter lack of diplomatic experience, Mr. Tillerson's cozy ties to Vladimir Putin and Russia would represent an untenable conflict at the State Department," he said.

Leading senators including McCain on Monday threw their backing behind a congressional investigation into US intelligence assessments on Russia election interference, putting top Republicans on a collision course with the incoming president.

The president-elect has dismissed the intelligence reports about Russian interference as "ridiculous," defying an increasing number of senators from his own party, as well as top Democrats, the Central Intelligence Agency and the outgoing White House.

Tillerson bested eight or nine contenders for the job of secretary of state, including former CIA director David Petraeus, former UN ambassador John Bolton, Senate Foreign Relations Chairman Bob Corker and erstwhile Trump critic and former Massachusetts governor Mitt Romney.

Former US secretary of state Condoleezza Rice and former defense secretary Bob Gates, who have done consultancy work for ExxonMobil, praised the choice.

"He will bring to the post remarkable and broad international experience; a deep understanding of the global economy; and a belief in America's special role in the world," Rice said.