"I am going to be sending (Sessions) a letter to have him explain himself, but he made a bald statement that during the campaign he had not met with the Russians," Franken said on CNN's "New Day." "That's not true."
In the aftermath of revelations that Sessions twice met with Russian ambassador Sergey Kislyak at a time when Moscow was suspected of engaging in hacks against Hillary Clinton and the Democratic National Committee, Democratic lawmakers and a number of their Republican colleagues on Capitol Hill have called on the attorney general to remove himself from any role in overseeing any investigation related to Russia.
Sessions has strongly pushed back against the reports, saying he never discussed campaign-related issues with anyone from Russia.
"I never met with any Russian officials to discuss issues of the campaign," he said in a statement Wednesday night. "I have no idea what this allegation is about. It is false."
Asked by NBC News Thursday morning if he would recuse himself in investigating any potential ties between Trump's campaign and Russian officials, Sessions said he would do so "whenever it's appropriate."
Franken on Thursday stopped short of calling for Sessions' ouster, as top Democrats Rep. Nancy Pelosi and Sen. Chuck Schumer have.
But the Minnesota senator, whose questioning during the confirmation hearing ultimately led Sessions to deny having any contact with the Russians, said the attorney general had presented conflicting explanations.
"First, it is 'I didn't meet with any Russians,' then it's 'I met with the Russian ambassador, but I don't remember what we discussed,' and then it's ... 'We didn't discuss the campaign,'" Franken said. "These are all contradictory."
Franken insisted that his line of inquiry had been simple and -- in a turn of phrase that recalled his time as a comedian -- recalled the exchange with Sessions with some curiosity.
"I had simply asked him what would he do if he had learned that other members of the campaign had met with the Russians, hoping he would say he would recuse himself. He chose not to answer that, but instead chose to say that he had not met with the Russians," Franken said.
He then added: "And, of course, the ambassador from Russia is a Russian."