Rex Tillerson, the former chairman and chief executive of Exxon Mobil, has been sworn in as the United States’ secretary of state.

Tillerson, who has never held political office, succeeds John Kerry as the US top diplomat.

He was Wednesday night sworn in by Mike Pence, the vice-president, in the oval office.

The former oil chief had been criticised for his ties to Russia, owing to his role in multibillion-dollar deals with Russia’s state oil company, Rosneft.

His critics had opined that suggested Tillerson, who was awarded the Order of Friendship by the Kremlin in 2013, would not be able to give up his corporate interests.

Tillerson’s confirmation took weeks of intense scrutiny and vetting before coming to fruition — and the votes which ushered him into office were mostly from Republicans.

While the former ExxonMobil executive was waiting for the senate to confirm him, Trump imposed a major travel ban on seven Muslim countries and sparked a diplomatic row with Mexico by threatening to send US troops over the border.

During the swearing in ceremony, Donald Trump, US President, told Tillerson that, “your whole life has prepared you for this moment.”

Tillerson replied, saying, “As I serve this president, I will always represent the interests of the American people at all times.”