PHOENIX — Saying the busing is illegal, state Attorney General Tom Horne threatened today to sue federal officials for dropping off undocumented individuals they apprehended in Texas in Tucson and Phoenix.

In a letter to Homeland Security Secretary Jeh Johnson, Horne said he can find no legal authority "for such arbitrary and injurious actions." In fact, Horne said transporting illegal immigrants for any purpose other than to federal facilities violates the law.

Beyond that, Horne contends that moving the undocumented individuals from Texas to Arizona violates federal law which requires Johnson's agency "to control and guard the boundaries and borders of the United States against the illegal entry of aliens."

Horne's move came just as Johnson was detailing for the media the efforts his agency is making to deal with the separate but related problem of the flood of unaccompanied minors who also have been picked up crossing the border into Texas.

Johnson insisted that his agency is doing what it can, as quickly as possible to process the children and turn them over to the Department of Health and Human Services. He said that agency provides a "safe and secure environment."

He did not specifically address the allegations made Wednesday by immigrant rights groups that there is "systemic abuse" of children who come into the custody of Customs and Border Protection.

But, in a warning to parents not to send their children to the United States, he said that a processing center for those who enter the country illegally "is no place for children."

CBP Commissioner Gil Kerlikowske, speaking at the same news conference in Washington, promised that the allegations will be investigated. But Kerlikowske praised what he said have been the "absolutely heroic efforts" of his officers to deal with the unexpected surge in border crossings.

Meanwhile, Gov. Jan Brewer was scheduled to send a staffer to Nogales today to check on conditions there where unaccompanied children, brought in from Texas, are being temporarily kept until they are turned over to Health and Human Services.

But Brewer also used the problem to send out an email today to not only sign a petition to the president to express outrage over immigrants being bused to Arizona but also to solicit donations to Jan PAC, her federal political action committee which paid for the message.