Gov. Jan Brewer said Friday that most illegal immigrants entering Arizona are being used to transport drugs across the border, an assertion that critics slammed as exaggerated and racist.

Brewer said the motivation of "a lot" of the illegal immigrants is to enter the United States to look for work, but that drug rings press them into duty as drug "mules."

"I believe today, under the circumstances that we're facing, that the majority of the illegal trespassers that are coming into the state of Arizona are under the direction and control of organized drug cartels and they are bringing drugs in," Brewer said.

"There's strong information to us that they come as illegal people wanting to come to work. Then they are accosted and they become subjects of the drug cartel," she said.

Brewer's office later issued a statement in response to media reports of her comments. It said most human smuggling into Arizona is under the direction of drug cartels, which "are by definition smuggling drugs."

"Unless Gov. Brewer can provide hard data to substantiate her claim that most undocumented people crossing into Arizona are 'drug mules,' she must retract such an outrageous statement," said Oscar Martinez, a University of Arizona history professor whose teaching and research focuses on border issues. "If she has no data and is just mouthing off for political reasons, as I believe she is doing, then she must apologize to the people of Arizona for lying to them so blatantly."

Sen. Jesus Ramon Valdes, a member of the Mexican Senate's northern border affairs commission, called Brewer's comments racist and irresponsible.

"Traditionally, migrants have always been needy, humble people who in good faith go looking for a way to better the lives of their families," Ramon Valdes said.

A Border Patrol spokesman said illegal immigrants do sometimes carry drugs across the border, but he said he couldn't provide numbers because smugglers are turned over to prosecutors.

"I wouldn't say that every person that is apprehended is being used as a mule," spokesman Mario Escalante said from Tucson. "The smuggling organizations, in their attempts to be lucrative and to make more money, they'll try pretty much whatever they need."

T.J. Bonner, president of the union that represents border agents, said some illegal border-crossers carry drugs but most don't. People with drugs face much stiffer penalties for entering the U.S. illegally, and very few immigrants looking for work want to risk the consequences, Bonner said.

"The majority of people continue to come across in search of work, not to smuggle drugs," he said. "Most of the drug smuggling is done by people who intend to do that. That's their livelihood."

A spokesman for a human rights group said Brewer's comments were "an oversimplification of reality."

"We have some stories of people being forced to carry drugs," said Jaime Farrant, policy director for Tucson-based Border Action Network. "We disagree with the assessment that people are crossing (to carry drugs). We have no evidence that's the truth. We think most people come in search of jobs or to reunite with their families."

Brewer spoke Friday when asked about comments she made in a recent election debate among Republican candidates for governor.

She said during the June 15 debate that she believed most illegal immigrants were not entering the United States for work. She then associated illegal immigrants with drug smuggling, drop houses, extortion and other criminal activity.

Brewer on April 23 signed a controversial new state immigration enforcement law that is scheduled toe effect July 29, although five legal challenges already are pending in federal court, and the U.S. Justice Department may file its own challenge.

The Arizona law requires police officers enforcing another law to question a person's immigration status if there's a reasonable suspicion that the person is in the country illegally.

Francisco Loureiro, who has run a migrant shelter for more than 20 years in Nogales, Sonora, across the border from the Arizona town of the same name, said Brewer's comments are aimed at turning the people of Arizona against migrants and strengthen support for the state's new law.

"That governor is racist and she has to look for a way to harm the image of migrants before American society and mainly before the people of Arizona," Loureiro said.

Roberto Suro, a University of Southern California journalism professor who founded a research center on Hispanics, said he was skeptical of Brewer's assertion, partly because federal authorities would be trumpeting many more drug seizures than they do. "The Border Patrol is not secretive about saying when they apprehend 10 people and found knapsacks (containing drugs) nearby," he said.

Attorney General Terry Goddard, the presumptive Democratic nominee for governor, said Brewer "does not understand the difference between illegal immigration and the organized criminals who are members of the violent drug cartels who pose a very a real danger."

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Associated Press writers Jonathan J. Cooper in Phoenix and Olga R. Rodriguez in Mexico City contributed to this report.