The US Senate Foreign Relations Committee has started a confirmation hearing for Rex Tillerson, President-elect Donald Trump's choice for the next Secretary of State.

Tillerson, the longtime chief executive of the multinational oil and gas corporation ExxonMobil, said that he would recommend a "full review" of the US-Iran nuclear deal reached under President Barack Obama's administration in 2015.

With no prior government experience, 64-year-old Tillerson is the target of much criticism from Democrats and Republicans who have not joined the Trump camp of the party.

Speaking in his Senate confirmation hearing, Tillerson said that he did not oppose the Trans Pacific Partnership free trade deal, but said he shared some of Trump's views about whether the pact as negotiated reflected all the best interests of the United States.

The hearing comes at a time when Trump has come under increasing criticism over alleged ties to Russia's President, Vladamir Putin.

Tillerson, who has business ties to Russia, faced a grilling on his views of Putin and tough questioning from Republican Senator Marco Rubio about whether he believed Putin was a war criminal.

Rubio specifically referred to Russia's military actions in the Syrian civil war, where it has provided military support for the Syrian government.

"I would not use that term," Tillerson said.

Sanctions questioned

Tillerson also declined to say whether he would support upholding President Obama's executive order imposing fresh sanctions, which was in retaliation for what Washington says was Moscow's hacking and other efforts to tilt the 2016 presidential election in Trump's favour.

Tillerson said that it was "a fair assumption" that Putin was aware of Russian efforts to interfere in the US election.

He said cyber-activity by the Russian government, as well as other "bad actors", undermined the democratic process in the US.

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The hearing was interrupted by sporadic protests.

Tillerson's confirmation hearing comes at a time of rising tensions with Russia.

US intelligence agencies have concluded that Russia was behind the hacks of political figures in an effort to help the Republican Trump defeat Democratic candidate Hillary Clinton in the November 8 election. Moscow has denied the allegations.

In another revelation, also denied by Moscow, two US officials said on Tuesday that classified documents presented last week to Trump by the heads of four US intelligence agencies included claims that Russian intelligence operatives have compromising information about him. Trump dismissed the reports, first made by CNN, as "fake news".

Tillerson opposed US sanctions against Russia in 2014 over its annexation of Crimea from Ukraine because he said he thought they would be ineffective.