Maricopa County Sheriff Joe Arpaio listens to one of his attorneys during a news conference on April 3 in Phoenix. (Ross D. Franklin/AP)

The standoff between the federal government and a high-profile Arizona sheriff accused of discriminating against Hispanics escalated Tuesday when settlement negotiations fell through and the Justice Department threatened to sue the sheriff.

Justice officials have accused Maricopa County Sheriff Joe Arpaio’s department of illegally detaining Hispanic residents and denying them critical services in jail. A day before settlement negotiations were to begin, Arpaio refused to agree to a court-appointed monitor to oversee changes in his department, one of the Justice Department’s requirements.

“We believe that you are wasting time and not negotiating in good faith,” wrote Deputy Assistant Attorney General Roy L. Austin Jr. in a letter to Arpaio’s attorney. “Your tactics have required DOJ to squander valuable time and resources.”

Arpaio, who calls himself “America’s toughest sheriff,” has been criticized for forcing inmates to dress in pink underwear and work on chain gangs. But he is seen as a kind of folk hero to those who favor his tough tactics and his much publicized “crime sweeps” of mostly Hispanic neighborhoods.

The federal investigation of Arpaio’s department began in 2008. In December, the Justice Department accused Arpaio’s department of violating the civil rights of Hispanics, saying in a report that the officers have engaged in a “pattern or practice of unconstitutional policing” by unlawfully stopping, detaining and arresting Hispanics.

Once in jail, the report said, Hispanics are punished if they fail to understand commands in English and are denied access to basic services such as new clothes, sheets or information about early-release programs.

Arpaio’s department is under a separate criminal investigation. A federal grand jury in Phoenix is looking into whether Arpaio used his power to investigate and intimidate political opponents and whether his office misappropriated government money.

Arpaio and his lawyers have denied any racial profiling and have said Justice Department investigations are politically motivated.

Justice officials said this is the second time Arpaio’s attorneys canceled negotiations at the last minute. They were scheduled to meet with the attorneys on March 1, but the meeting was canceled. Instead, on that day, Arpaio held a news conference, saying that President Barack Obama’s birth certificate was a forgery and calling for a federal investigation.

Joseph J. Popolizio, an attorney for the Maricopa County sheriff, could not be reached for comment.

In his letter, Austin said that a monitor of the sheriff’s department was a non-negotiable element for a settlement agreement.

“DOJ considers the oversight of an independent monitor to be an absolute necessity for meaningful and sustainable reform” of the Maricopa County Sheriff’s Office, Austin wrote.

The investigation of Arpaio and his department is one of 17 probes the Justice Department’s Civil Rights Division is conducting of police and sheriff departments — the most in its 54-year history. Other departments being investigated include those in New Orleans; Newark; Seattle; Puerto Rico; Portland, Ore.; and East Haven, Conn.

“We hope to resolve the concerns,” said Thomas E. Perez, assistant attorney general for civil rights. “But we will not hesitate to take appropriate legal action if the [Maricopa County Sheriff’s Office] chooses a different course of action.”