Vice President Joe Biden met privately with Massachusetts Sen. Elizabeth Warren at his Washington, D.C., residence Saturday, CBS News has confirmed.

Biden's meeting with the prominent Democrat is the strongest sign yet that the vice president is becoming more serious as he considers a potential bid for the White House in 2016.

A source with knowledge of the gathering told CBS News that Biden met with the Democratic senator at the vice president's request. Biden was officially scheduled to spend the weekend at his Delaware home, but he arrived in Washington early Saturday.

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Biden, 72, has flirted with the idea of a presidential campaign for some months. And since the death of his son Beau Biden in May, there has been an outpouring of support for the vice president.

In Beau Biden's final days, he reportedly begged his father to run, telling him, "Dad, it's who you are."

If Biden decides to enter the race, he would be presenting a challenge to Democratic front-runner Hillary Clinton with just over five months until the first early voting contests in Iowa and New Hampshire.

Biden will be returning to Delaware Saturday night.