Human rights groups demanded information Tuesday about the whereabouts of a missing activist who was last seen when Argentine border police evicted a group of Mapuche Indians from lands in Patagonia owned by Italian clothing company Benetton.

Santiago Maldonado's family says he went missing Aug. 1, when he was taking part in a protest supporting the land claims by the indigenous Mapuche community. They say border police detained him when he was blocking a road with other protesters in Chubut province, about 1,100 miles (1,800 kilometers) southeast of Argentina's capital.

Authorities deny any wrongdoing. Argentina's Security Ministry offered a $27,000 reward on Tuesday for information on Maldonado's location.

Maldonado's disappearance has triggered violent protests in Argentina, where some 30,000 people died or were forcibly disappeared during the 1976-1983 military dictatorship, according to human rights groups.

"It's inadmissible that in a rule of law, security forces take part in the detention and forced disappearance of people," Estela de Carlotto, president of the Grandmothers of the Plaza de Mayo human rights group, said at a news conference.

Participants in the Aug. 1 demonstration were demanding the release of Facundo Jones Huala, an imprisoned Mapuche leader who is wanted by Chile. The lands belong to Compania de Tierras Sud Argentino, a wool-producing company owned by Benetton. Mapuches claim the lands as their ancestral territory and have been occupying them since 2015.

"On the day Maldonado disappeared, about 100 agents from the Gendarmerie entered the indigenous community shooting rubber and lead bullets, taking no precautions to protect its members' lives or integrity," the human rights group Center for Legal and Social Studies said Tuesday.

Argentine activist Adolfo Perez Esquivel, who won the Nobel Peace Prize in 1980 for his defense of human rights during the dictatorship, accused the government of repressing indigenous peoples.