PHOENIX (Reuters) - Arizona's two U.S. senators on Thursday expressed concern over media reports accusing Maricopa County Sheriff Joe Arpaio, best known for his crackdown on illegal immigration, of giving short shrift to hundreds of sex-crime investigations.

In a joint statement, Republican Senators John McCain and Jon Kyl said the cases in question, some involving children, deserved to be taken seriously, and that they would support federal assistance in examining the cases if necessary.

"Victims of abuse not only deserve the respect of law enforcement, but their rights must also be protected throughout the criminal justice process," the senators said in their one-paragraph statement. "Laws that we have championed are intended to give a voice to victims of crime."

The two high-ranking Republicans weighed in following criticism against the conservative Arpaio from a Democratic congressman and two other Democrats in the state Legislature over the sex crimes cases. Republican politicians had previously held back on commenting.

Arpaio, whose jurisdiction as Maricopa County sheriff encompasses Phoenix and surrounding areas, came under fire for media reports by the Associated Press, the Arizona Republic and others saying his office had botched investigations of hundreds of sex-crime complaints from about 2005 to 2007.

The McCain-Kyl statement stopped short of accusing Arpaio of wrongdoing and did not mention the Republican sheriff by name.

But the pair said they would support any requests for assistance from the U.S. Justice Department to "properly investigate and prosecute these and other cases, including those which need to be investigated by other law enforcement agencies."

The tough-talking Arpaio has previously stirred controversy, and faces a federal civil rights inquiry, for his department's crackdown on illegal immigrants.

Arpaio has apologized for any problems with sex crime investigations and vowed to hire a national expert to bolster training for his investigators and those in other nearby law enforcement agencies.

He said his office is not the only police agency dealing with such difficulties.

"I appreciate the offer of assistance by Senators McCain and Kyl to help this office and other major law enforcement agencies in the (Phoenix) Valley that currently have the same problem we did back in 2007," Arpaio said in a statement on Thursday.

Several Democratic lawmakers have called on Arpaio to resign citing the allegedly botched investigations.

U.S. Representative Raul Grijalva of Arizona on Monday said Arpaio should leave office immediately, charging that his attitudes as Sheriff represent "the worst kind of unaccountable arrogance."

"Mr. Arpaio might love headline-grabbing crackdowns and theatrical media appearances, but when it comes to the everyday work of keeping people safe, he seems to have lost interest some time ago," Grijalva said.

Arpaio said he would not resign, charging that his staunchest critics are Democrat foes of his immigration policies who are seizing on questions raised about the sex crime investigations.

(Editing by Alex Dobuzinskis, Steve Gorman and Peter Bohan)

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