Story highlights Coons told Erin Burnett the the Trump team's defense "does strain credibility"

Coons said he hasn't decided whether he will vote to confirm Rex Tillerson as secretary of state

(CNN) Sen. Chris Coons said Friday that it "seems very suspicious" that President-elect Donald Trump's pick for national security advisor spoke to Russia's ambassador to the United States on the same day the Obama administration announced sanctions against Russia for alleged hacking during the presidential election.

An official with the Trump transition team said the ambassador texted retired Army Lt. Gen. Michael Flynn on December 28, the day before sanctions were announced, and the two spoke by phone the next day. The official insists sanctions were not discussed, and the phone call focused on how to connect Trump with Russian President Vladimir Putin after the inauguration.

In an interview on CNN's "Outfront," Coons, a Democrat from Delaware who sits on the Senate Foreign Relations Committee, told Erin Burnett the Trump team's defense "does strain credibility" and that "it seems very suspicious that three weeks in advance, he (Flynn) needed to have a call in order to schedule a call that wouldn't happen for weeks."

Coons said once Trump takes office, however, Flynn is free to choose which foreign countries and ambassadors he makes contact with.

Coons said Flynn's conversations are the latest in a series of developments that "raise real questions" about Trump's nomination of former ExxonMobil CEO Rex Tillerson to be the next secretary of state.

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