By Nicole Gaouette CNN

WASHINGTON (CNN) -- President-elect Donald Trump's nominee to be the US envoy to the world drew a sharp line between his views and those of his future boss, denouncing Russian aggression in cyberspace and in Ukraine.

RexTillerson was asked at his Senate Foreign Relations Committee confirmation hearing whether he believed that Russia had hacked US elections -- a charge Trump has consistently denied or played down.

The former ExxonMobile CEO also condemned Russia's invasion of Ukraine as an "illegal action" and said he would have sent the country defensive weapons to use against Moscow, a step the Obama administration did not take. And he praised the usefulness of sanctions as a deterrent, but cautioned that their use can hurt American businesses.

"In diplomacy it is useful to have a stick that is in your hand so that whether you use it or not, it becomes part of that conversation," Tillerson said.

Tillerson said he hadn't received any classified briefings on the Russian hacks.

He that it's a "fair assumption" that Vladimir Putin authorized the attacks.

Tillerson made the remarks amid controversy about a CNN report that Russia may have compromising information about the President-elect.

He also took steps in his opening remarks to strike a tougher line on Moscow than Trump has to date, saying that "Russia must know that we will be accountable to our commitments and those of our allies, and that Russia must be held to account for its actions." 

Even so, Democrats -- and one Republican -- came out swinging.

Democrats questioned Tillerson's failure in his prepared opening remarks to mention Russia's alleged hacking of US elections, his views on human rights and climate change, and ExxonMobil's ties to Russia.

Florida Republican Sen. Marco Rubio went after Tillerson about Russia's violations of human rights and its alleged war crimes in Syria, telling the nominee that he found it "discouraging" when Tillerson wouldn't label Moscow's actions in Aleppo.

"You are still not prepared to say that Vladimir Putin and his military have violated the rules of  war and have conducted war crimes in Aleppo," Rubio declared, pointing to information in the public record about civilians being targeted in the Syrian city.

"Those are very, very serious charges to make, and I would want to have much more information before reaching a conclusion," Tillerson demurred.

Maryland Sen. Ben Cardin, the ranking Democrat on the committee, pointed to Trump's refusal to acknowledge the intelligence community's assessment about Russian hacking and asked Tillerson what he would do about it.

"We need to stand up to that bully in Moscow," Cardin said.

Cardin said he would be quizzing Tillerson on ExxonMobil's business deals with Russia, indicating that they "supported directly or indirectly" some of Putin's more aggressive activities.

"It's not too great of a distance from Exxon business partnerships to Putin's slush funds" for disinformation and other activities, Cardin charged.

The former ExxonMobil CEO claims close ties to Putin, having overseen the company's partnership with a state-owned energy giant there, work that earned him the country's highest award for non-citizens.

Former Secretary of Defense Bob Gates, who introduced Tillerson to the committee, noted that "much has been said about Mr. Tillerson and Russia." He went on to say that the secretary of state job requires resisting Russian aggression and containing the risk of conflict.

Referring to the Russian president, he said that "this new administration must thread the needle between pushing back against Vladimir Putin's aggression, meddling, interventionism, ambitions and bullying, and at the same time, find a way to stop the dangerous downward spiral in our relationship with Russia." He added that "Tillerson is the right person at the right time."

In opening remarks that were interrupted by a shouting protestor, the nominee tried to strike a balance, saying that "where cooperation with Russia based on common interests is possible, such as reducing the global threat of terrorism, we ought to explore these options," Tillerson said. "We need an open and frank dialogue with Russia regarding its ambitions, so that we know how to chart our own course."

But he added that "Russia must know that we will be accountable to our commitments and those of our allies, and that Russia must be held to account for its actions." 

And he validated NATO allies' concerns about Russian aggression but said that some of the blame lies with the Obama administration. The US "sent weak or mixed signals with 'red lines' that turned into green lights," Tillerson said. "We did not recognize that Russia does not think like we do."

The dark-horse candidate for the Foggy Bottom post has already prompted concerns from human rights groups that cite his former company's practices and lawmakers who charge that he has a track record of putting profits before US interests, with one saying he could be a "disaster" as secretary of state.

Tillerson's big moment in the spotlight comes as CNN reported Tuesday that US intelligence agencies are investigating reports that Russia collected sensitive and potentially compromising information about Trump's personal and financial affairs.

The information, from a firm run by a former British intelligence operative, also indicated that throughout the campaign, Trump surrogates were in touch with intermediaries for the Russian government. Sen. John McCain, an Arizona Republican, became aware of the information in December and passed it to FBI Director James Comey that month.

Republicans will be key to Tillerson's ability to get through the Foreign Relations Committee and to the Senate floor, where his nomination needs 51 votes to pass. The committee is controlled by Republicans, who hold 10 of the 19 seats. If all Democrats oppose him and they're joined by just one Republican, Tillerson could stall there.

Tillerson's emergence as a candidate for the post

The oil man, who had headed the ExxonMobil empire since 2006 until retiring at the end of last year, began his journey to Washington in Texas. He was born and educated there, and spent his adult life inside the company, starting in 1975 as a production engineer after graduating from the University of Texas at Austin. He's never worked anywhere else.

Tillerson emerged as a candidate for secretary of state after high-profile national security Republicans -- all of whom had worked for the oil company at some point -- recommended him to Trump. Former Secretaries of State Condoleezza Rice and James Baker, former National Security Adviser Stephen Hadley and Gates, the former Defense Secretary, sang Tillerson's praises.

He eventually won out over more well-known figures, including former Republican presidential candidate Mitt Romney and ex-UN Ambassador John Bolton. After Tillerson's nomination was announced, Washington watchers began sifting through his company's record for clues as to how he might perform on the world stage.

Tillerson built his career on exploration with Russian energy giant Rosneft, making Russia ExxonMobil's largest exploration theater. Russian officials hailed the announcement of Tillerson's nomination.

CNN's Elise Labott and Matt Egan contributed to this report.

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