It's official: Newark Mayor Cory Booker is running for the United States Senate seat currently held by Frank Lautenberg.

(Photo by Alex Wong/Getty Images)

Booker took the first formal step towards a campaign by filing papers with the Federal Election Commission on Tuesday. The Democrat posted a video before Christmas announcing he was going to "explore" a run for US Senate that took him out of the running for Governor.

Lautenberg has not indicated any plans to retire from the Senate.   When Booker expressed interest in the seat last month, Lautenberg's spokesman said the senator would consider his options later. Booker said earlier this week he has tried unsuccessfully to reach out to Lautenberg; a meeting was cancelled as Congress dealt with the fiscal cliff.

Sixth District Congressman Frank Pallone (D) has expressed interest recently in making a run for Lautenberg's seat as well but not until the second financial relief from Sandy is approved.

The Associated Press contributed to this story.