Rio de Janeiro (AP) — Gunmen opened fire Saturday on a group of indigenous people in Brazil’s Maranhao state, killing two, according to the state’s public security secretariat.

The attack on members of the Guajajara group, known for its forest guardians who protect their territory against illegal deforestation, occurred on the margins of a federal highway near El-Betel village. The assailants lowered the car’s windows and immediately started shooting, Magno Guajajara, a local leader, told the Associated Press.

The incident comes during the U.N.’s two-week international climate change conference in Madrid, where Brazilian indigenous leaders are present and attempting to draw attention to the importance of protecting their forest territories. Last month, one of the Guajajara’s forest guardians was killed.

“How long will this go on? Who will be next?” Sonia Guajajara, coordinator of a network to connect Brazilian indigenous peoples, said in a phone interview from Madrid. “The authorities need to look at our indigenous people. They’re taking away our lives.”

Brazil’s federal police are investigating the killing in El-Betel and its motivation, Justice Minister Sergio Moro said on social media. Moro also said he is evaluating the possibility of dispatching a National Guard team to the state.