The U.S. Department of Justice announced here Thursday that it has filed suit against Maricopa County Sheriff's Office and its flamboyant head, Joe Arpaio, for discriminating against Hispanics.

Arpaio, who boasts of being America's toughest sheriff, is known for his zealous pursuit of undocumented immigrants.

"MCSO officers have unlawfully discriminated against Latinos and violated their constitutional rights in a number of ways," Assistant Attorney General Thomas E. Perez told a press conference in Phoenix.

The discriminatory practices include racial profiling of Latinos during traffic stops, "unlawful detention, searches and arrests of Latino drivers and passengers, and unlawful targeting and illegal detention of Latinos during home and worksite raids," Perez said.

"Constitutional policing and effective policing go hand-in-hand," the assistant attorney general said. "Our complaint alleges that the defendants' actions were neither constitutional nor effective."

The lawsuit seeks to have MCSO barred from engaging in racial profiling and to obligate the agency to implement policies and training to avoid this type of conduct, which came to light during the course of an investigation.

On Dec. 15, the Department of Justice said it had found reasonable cause that MCSO and Arpaio violated the constitutional rights of Latinos.

Negotiations between the federal government and MCSO to avoid the lawsuit failed after Arpaio categorically refused to allow an independent monitor to be placed in his office.

The DOJ said it has also noted discriminatory practices in the county's jails against Latino inmates who speak little English.

It also accuses Arpaio of engaging in reprisals against people who criticize him, making them the target of investigations or administrative actions without any cause.

According to the DOJ investigation, Latino motorists have between four and nine times more chance of being arrested by MCSO than other drivers.

Arpaio, who has been sheriff since 1993, heads the only Arizona law enforcement agency to enforce the state's anti-coyote law, which penalizes undocumented migrants who admit to having paid people traffickers to get them into the United States and the state law that sanctions employers, punishing businesses that knowingly employ undocumented foreigners.

Anticipating the lawsuit, Arpaio on Wednesday presented a document in which he lists the steps his office will take to move closer to the local Latino community.

Among the areas that need to be improved are training, communication, safety, internal integrity, public information and creating a better record of the office's activities, among others.