The former Republican presidential candidate John McCain has been accused of "scapegoating" Mexicans over comments he made linking wildfires in his home state of Arizona to illegal immigration.

The issue ignited over the weekend when the US senator said there was "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".

Two other Arizona Republicans backed McCain, but immigration activists swiftly condemned his statement as typical of a "blame it on the Mexicans" mentality. Democratic politicians also waded in to rebuke McCain's politicisation of the issue.

"It's his constant refrain for everything that ails mankind," said Roberto Reveles, founder of Somos America, an Arizona-based immigrant 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."

Republican senator Jon Kyl and house representative Paul Gosar defended McCain, claiming they had been told some fires in the southern part of the state are started by illegal immigrants. They did not specify to which fires they were referring, but framed the resulting 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.

This assertion raised the hackles of Arizona Democrat and house representative Raul Grijalva. "They served this, they pandered it," he said. "And now [they] say that anybody who criticises that inappropriate, unsubstantiated claim somehow has a political agenda. This is a tragedy of huge proportions for Arizona. Those of us who criticise it are only reacting to what they started."

The debate raged as state authorities continued to assess the damage from a wildfire that burned in a heavily populated area near the Mexican border. About 10,000 people remain unable to return to their homes on the outskirts of Sierra Vista, about 15 miles north of the border, where on Sunday the so-called Monument fire swept off a mountain and destroyed 14 homes and four businesses. It has now destroyed 58 homes and burned through more than 40 sq miles (103 sq km) since it started a week ago.

Along the border with New Mexico, the biggest blaze in Arizona has charred an area five times that size, but has not done as much damage. Despite burning more than 800 sq miles since late May, the Wallow fire has destroyed just 32 homes and four rental cabins.

A third wildfire, the Horsehoe Two in the south-east of the state, is now 80% contained after charring more than 330 sq miles and destroying 23 structures. Officials say all three blazes are the result of human activity, but no one has yet been charged and no further details have been issued.