Donald Trump has formally announced Rex Tillerson, Exxon-Mobil chairman and chief executive, as his nomination to serve as secretary of state.

According to the New York Times, citing "people familiar with the president-elect's final choice", former Massachusetts governor Mitt Romney, retired General David Petraeus and Senator Bob Corker of Tennessee all have been told over the phone that they were being passed over in favour of Tillerson.

Referring to Tillerson, Trump, in a statement released on Tuesday by his transition team, said: "His tenacity, broad experience and deep understanding of geopolitics make him an excellent choice for secretary of state.

"He will promote regional stability and focus on the core national security interests of the United States."

In an accompanying statement, Tillerson said he was "honoured" by his selection and shares Trump's "vision for restoring the credibility of the United States' foreign relations and advancing our country's national security".

Trump also said that as the nation's top diplomat, Tillerson would be "a world-class leader" working on behalf of the American people.

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Politicians from both major parties have previously raised questions about Tillerson's ties to Russia, having met President Vladimir Putin several times.

In 2013, Putin bestowed a Russian state honour, the Order of Friendship, on Tillerson, citing his work "strengthening cooperation in the energy sector".

Senator John McCain, a leading foreign-policy voice and 2008 Republican candidate for president, told Reuters in an interview: "I have concerns. It's very well known that he has a very close relationship with Vladimir Putin."

Calling Putin "a KGB agent who is bent on restoring the Russian Empire", McCain said that he would await confirmation hearings if Tillerson is nominated before making a judgment on the nomination.

Worries voiced

Another Republican, Senator Marco Rubio, who serves on the Senate Foreign Relations Committee that would review a Tillerson nomination, has voiced similar worries.

Renewed allegations of Russian hackers meddling in the November 8 election, coupled with Trump's stated admiration of Putin, have stoked concern.

The US is at odds with Russia over a range of issues that include Syria, Ukraine and NATO's presence in Eastern Europe.

US intelligence previously linked Russia to damaging email leaks from the Clinton campaign, but saw it as a broad effort to undermine confidence in the US political process.

Source: Al Jazeera and news agencies