Newark, New Jersey Mayor Cory Booker speaks during day one of TechCrunch Disrupt SF 2012 event at the San Francisco Design Center Concourse in San
Newark, New Jersey Mayor Cory Booker speaks during day one of TechCrunch Disrupt SF 2012 event at the San Francisco Design Center Concourse in San Francisco, Calif., September 10, 2012. (REUTERS/Stephen Lam)

NEWARK, N.J.  Newark Mayor Cory Booker announced his candidacy on Saturday for a U.S. Senate seat for New Jersey and will run in a Democratic primary set for August to fill the seat of the late Senator Frank Lautenberg.

"I do not run from challenges. I run towards them," Booker said at a news conference in the city where he has served as mayor since 2006.

After the death of Lautenberg, 89, on Monday, Republican Governor Chris Christie called a special election to fill the remainder of the late senator's term.

Booker had previously announced his intention to seek the seat when Lautenberg's term expired in 2014.

Booker enters the primary race against U.S. Representative Rush Holt, a seven-term congressman. Representative Frank Pallone Jr. of Long Branch is also widely expected to enter the Senate race.

Democrats criticized Christie's decision to hold a special election, calling it a calculated attempt by the governor to avoid appearing on the same ballot as Booker, who is among the state's most popular Democrats.

The special election, including the August primaries and the general election three weeks ahead of the normally scheduled November election, will cost the state about $24 million.

Christie dismissed the criticism, saying New Jersey should have a voter-approved representative in the Senate as soon as possible.

On Thursday, Christie appointed a fellow Republican, the state's attorney general Jeffrey Chiesa, to fill the seat until the general special election in October. Chiesa said he would not compete for the seat in the special election.