An elderly couple whose family's landholdings in southern Chile have long been targeted by indigenous Mapuche people were killed in an arson attack on Friday. The president, Sebastián Piñera, quickly flew to the scene and announced fresh security measures, including the application of Chile's tough anti-terrorism law and the creation of a special police anti-terror unit backed by Chile's military.

No one claimed responsibility for the attack, which some Mapuche people repudiated as abhorrent. But Chile's interior minister said pamphlets condemning police violence and demanding the return of Mapuche lands were left at the scene. The presidentially appointed governor of the remote southern region of Araucania, Andres Molina, called the attackers "savages".

"This attack affects the entire country and causes gigantic damage, for the pain and the delays that it means for thousands of families who want to live in peace," Piñera said. "This government is united in its effort to combat terrorism that affects the region. We will not hesitate to apply the full weight of the law."

"It should be completely clear," Piñera added, "that this fight is not against the Mapuche people. It's with a minority of violent terrorists who must be fought with everything the law allows."

The regional police chief, Ivan Bezmalinovic, said the fire was started after Werner Luchsinger, 75, fired a weapon in self-defence and struck a man from the nearby Mapuche community of Juan Quintrupil.

Luchsinger's wife Vivian McKay called relatives for help during the attack, but when they arrived just 15 minutes later the house was already in flames and she didn't answer her phone, according to the victim's cousin, Jorge Luchsinger.

The attack began on Thursday night as one of many political protests around Chile commemorating the death five years ago of Mapuche activist Matias Catrileo, who was shot in the back by an officer who served a minor sentence and then rejoined the police. The Indians scattered pamphlets related to the anniversary while on the Luchsinger property, Andres Chadwick, the interior minister, said.

The victims' Lumahue ranch is just 16 miles (25 kilometres) from the spot where Catrileo was killed on 3 January 2008.

Many of Chile's Mapuche activist groups were silent on Friday about the murders, repeating instead their complaints about continuing police violence of the kind that killed Catrileo years ago.

But Venancio Conuepan, who described himself as a law student who comes from a long line of Mapuche leaders, wrote an editorial on Friday condemning the violence, rejecting the idea that armed conflict can win their demands, and calling for the killers to be identified and tried in court. He said the vast majority of the Mapuche people agree with him.

"Enough of people using violence in the name of the Mapuche people. Our grandfathers never covered their faces. The Mapuche created parliaments, and always put dialogue first," wrote Conuepan on Radio BioBio's web site, titling his editorial, "Although you don't believe me, I'm Mapuche and I'm not a terrorist."

The Luchsinger family has been among the most outspoken in defending the property rights of the region's landowners against ancestral land claims by the Mapuche. But Jorge said his cousin had taken a lower profile and refused police protection.

Lorena Fries, the director of Chile's official Human Rights Institute, warned Friday against cracking down using the anti-terror law, which allows for holding suspects in isolation without charges, using secret witnesses and other measures that have been discredited by Chile's courts in previous cases of Mapuche violence. Instead, she said Piñera should reach out to the Indians, and honor their demands for self-governance and the recovery of ancestral land. "Something has to be done so that everyone puts an end to the violence," she said.

The Mapuches' demands for land and autonomy date back centuries. They resisted Spanish and Chilean domination for more than 300 years before they were forced south to Araucania in 1881. Many of the 700,000 Mapuches who survive among Chile's 17 million people still live in Araucania. A small fraction have been rebelling for decades, destroying forestry equipment and torching trees. Governments on the left and right have sent in police while offering programmes that fall far short of their demands.

The Luchsinger family also arrived in Araucania in the late 1800s, from Switzerland, and benefited from the government's colonization policies for decades thereafter, becoming one of the largest landowners in Chile's Patagonia region. Their forestry and ranching companies now occupy vast stretches of southern Chile, and impoverished Mapuches live on the margins of their properties.