A Costa Rican indigenous defender has been killed by an armed mob while trying to reclaim ancestral land – the latest in a spate of violence targeting native communities in Central America’s safest country.

Yehry Rivera, 45, from the Brörán community in Térraba, was shot dead around 11pm on Monday after being surrounded by a group of angry locals armed with sticks, machetes, stones and at least one gun.

The attack took place amid mounting tensions in Térraba, where human rights groups had warned authorities in recent days about non-indigenous groups violently confronting Brörán families reclaiming ancestral land.

The events leading up to Monday night’s fatal shooting remain unclear, but video footage seen by the Guardian shows members of the group throwing stones and insults over Rivera’s bleeding body, with a police car parked close by.

The killing comes just two weeks after Mainor Ortiz Delgado, 29, a leader of the Bribri indigenous people in neighbouring Salitre, was wounded in a gun attack, and less than a year since Sergio Rojas Ortiz, 59, was shot dead. Both cases remain unsolved.

Facebook Twitter Pinterest Yehry Helmut Rivera, an indigenous Brörán activist killed in Térraba, Costa Rica. Photograph: Hugo Navas

Costa Rica, an eco-tourism hub with five million inhabitants, is widely considered the region’s most equitable and law abiding country.

But in recent years, the Bribri and Brörán people have been subject to a string of violent attacks, racist harassment and trumped-up retaliatory lawsuits with almost total impunity. In 2013 Rivera survived a brutal beating while trying to stop illegal loggers. The alleged perpetrator was set free after being ordered not to return to Térraba for six months.

As a result, in 2015 the Inter-American Commission on Human Rights issued precautionary measures, calling on Costa Rican authorities to protect the lives and physical integrity of the Bribri and Brörán people. Rivera, Delgado and Ortiz were ostensibly recipients of these safety measures when attacked.

Amid growing international condemnation about the impunity, the government has pledged to investigate the growing list of crimes but denies responsibility for the spate of violence. President Carlos Alvarado condemned the murder on Twitter, and confirmed that one man had been detained.

“Early warnings about the growing tensions in Térraba were once again met with an ineffective response by the state,” said Vanessa Jiménez, a lawyer with the not-for-profit organization Forest Peoples Programme who works with the indigenous communities. “The government either can’t or won’t protect the Bribri and Brörán from violence.”

Latin America is the most dangerous continent in the world to defend land rights and natural resources, and indigenous communities often bear the brunt of the violence.

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Costa Rica has eight indigenous ethnic groups totalling 105,00 people who represent approximately 2.4% of the total population. There are 24 legally recognised indigenous territories, which are exclusively for communities with historical ties to the land, according to the 1977 Indigenous Act.

But the law has never been implemented.

As a result, the Bribri and Brörán people in the Puntarenas province, situated south-east of the capital San José, have taken matters into their own hands in recent years and retaken possession of some land through unauthorized occupations.

Despite some success, about 80% of half of the Brörán territory and almost half of Bribri territory remain occupied by non-indigenous families and farmers, who claim that their property and inheritance rights are being violated.

Grettel Navas, an indigenous Bröran who works at the Barcelona-based ENVJustice Project documenting environmental and land conflicts around the world, said: “Costa Rica enjoys an international image of a peaceful country, but this peace is not embracing all of us in the same way. Indigenous groups are victims of violence, discrimination and racism in their own lands … and victims of the inaction of the government.”