SIERRA VISTA - It always comes back to illegal immigration in Arizona - even when the state is on fire.

Sen. John McCain and other Republican politicians said Monday there was "substantial evidence" that border crossers were partly responsible for wildfires in the state. Fire officials say three major blazes in Arizona were started by humans, but they don't know any more details.

Activists swiftly jumped on McCain's statement as "scapegoating," saying that state leaders were merely deflecting attention away from the wildfire response.

The debate raged as people returned to homes Monday that had been evacuated near the U.S.-Mexico border. A day earlier the Monument Fire swept off a mountain into the outskirts of Sierra Vista, forcing thousands to flee.

Two other big fires - one in the Chiricahua Mountains and another in Eastern Arizona - blackened vast acreage and prompted their own evacuations.

Officials say all three blazes are the result of human activity. Whether illegal immigrants were involved - as has sometimes been the case - is unknown.

The issue heated up over the weekend when McCain told media: "There is substantial evidence that some of these fires have been caused by people who have crossed our border illegally. The answer to that part of the problem is to get a secure border."

The statement brought a quick reaction from activists.

"It's his constant refrain for everything that ails mankind," said Roberto Reveles, the founding president and a current member of Somos America, an Arizona-based immigration-rights group.

"It just seems like we have an epidemic of 'blame it all on the illegal aliens, blame it all on the Mexicans.' It's amazing that the public doesn't rebel against this type of scapegoating."

U.S. Rep. Raúl Grijalva on Monday condemned McCain for his statements claiming illegal immigrants were to blame for some of the state's wildfires.

"The atmosphere in Arizona is as toxic as I have ever seen it as a member of Congress," Grijalva said in a news release. "Every misfortune is blamed on undocumented immigrants. Senator McCain's comments continue to provoke an extreme anti-immigrant and anti-Latino atmosphere in Arizona. This level of intolerance has reached a new low."

A CNN report indicated McCain did not specify which fires had been started by illegal immigrants, nor did he identify his sources or provide details of the "substantial evidence" he cited.

McCain and fellow Arizona Republicans Sen. Jon Kyl and Rep. Paul Gosar released a joint statement Monday defending McCain, saying that they had been told that some fires in the southern part of the state were started by illegal immigrants. They did not specify to which fires they were referring but framed the debate as a distraction.

"While Arizonans continue to face the enormous challenges related to these wildfires, it's unfortunate that some are inserting their political agenda into this tragedy," their statement said.