(CNN) At the same time the FBI opened a probe into President Donald Trump for possible obstruction of justice after he fired FBI Director James Comey, counterintelligence agents were investigating why Trump was acting in ways that seemed to benefit Russia, according to a source familiar with the matter.

As CNN first reported, the FBI opened the Trump probe, in the hectic days after the President fired Comey, after considering various options for dealing with the firing.

It was a tense time. In addition to the Comey dismissal in May 2017, the President had raised concern in the FBI for comments he made to Russian officials in the Oval Office about firing his FBI director, according to the source familiar with the matter.

The source spoke to CNN after The New York Times reported Friday that law enforcement officials were so concerned they began investigating whether the President was working on behalf of Russia against US interests.

In a strongly worded reaction, White House press secretary Sarah Sanders said, "This is absurd. James Comey was fired because he's a disgraced partisan hack, and his Deputy Andrew McCabe, who was in charge at the time, is a known liar fired by the FBI. Unlike President Obama, who let Russia and other foreign adversaries push America around, President Trump has actually been tough on Russia."

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