Kentucky Governor Andy Beshear (D) on Tuesday called on Senator Mitch McConnell to "directly and verbally address the people of Kentucky" – or resign.

Beshear said McConnell must provide proof of his capacity to serve or resign.

"As Governor of the state you serve, I am calling on you to directly and verbally address the people of Kentucky and provide proof of your capacity to serve, or resign," Beshear wrote in a letter, CNN first reported.

"Per our research, a vacancy in the Senate occurs when a senator dies, resigns, or is expelled by a vote of the Senate itself," Beshear said.

"If you are unwilling to voluntarily show that you still have the capacity to serve, I will insist Leader Thune fully investigate your condition, report to the American people, and begin the process if warranted," Beshear wrote.

The Governor's letter comes after McConnell released his second 'proof of life' photo amid a 44-day absence from the Senate.

The latest photo is dated Sunday.