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MIAMI (CBSMiami) — Florida Senator Marco Rubio challenged President-elect Donald Trump’s pick for secretary of state over his relationship with Russia.

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Former ExxonMobil CEO Rex Tillerson faced a panel lawmakers Thursday, including Rubio who sparred with him over a contentious topic – Tillerson’s ties to Russian President Vladimir Putin.

In a steady line of questioning, Rubio grilled Tillerson on his thoughts on whether Putin is a war criminal prompting a tense exchange.

“Is Vladimir Putin a war criminal,” asked Rubio.

“I would not use that term,” replied Tillerson.

In return, Rubio said, “Well, let me describe the situation in Aleppo and perhaps that will help you reach that conclusion.”

Rubio went on to give details on how Putin directed the Russian military to conduct a “devastating campaign” that targeted schools and markets using “battlefield weapons” to kill thousands in the Syrian city of Aleppo.

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“So based on all this information and what’s publicly in the record about what’s happened in Aleppo and the Russian military, 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,” asked Rubio.

“Those are very, very serious charges to make and I would want to have much more information before reaching a conclusion. I understand there is a body of record in the public domain, I’m sure there’s a body of record in the classified domain. And I think in order to deal with a serious question like this…,” Tillerson was said before Rubio interjected.

“Mr. Tillerson, what’s happened in Aleppo is in the public domain, videos and the pictures are there,” said Rubio.

“I would want to be fully informed before advising the president,” said Tillerson.

Rubio replied, ‘There is so much information about what’s happened in Aleppo…there’s so much information out there, it should not be hard to say that Vladimir Putin’s military has conducted war crimes in Aleppo.”

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The two also touched on Russia’s involvement in the election hacking. Tillerson agreed with Rubio that it was a “fair assessment” that Putin may have had knowledge of Russia’s involvement.