Two Spanish journalists making a documentary about anti-poaching efforts and a third foreign national were killed in Burkina Faso after being kidnapped there on Monday, according to the authorities from the Western African nation and Spain. The killings come at a time of increasing violence in Burkina Faso and a deteriorating security situation in the Sahel, especially in the border area of Burkina Faso, Mali and Niger. Burkina Faso has seen attacks from many armed groups, several of them linked to the Islamic State and Al Qaeda in the Islamic Maghreb.Attackers on motorbikes have stormed countless villages, forcing residents to convert to Islam and sometimes killing them even when they do. Others have ambushed military patrols and killed members of the armed forces, and hundreds of schools have been forced to close because of the violence.Prime Minister Pedro Sánchez of Spain on Tuesday confirmed the deaths of the two Spanish journalists, whom he identified on Twitter as David Beriain and Roberto Fraile.The third victim remained unidentified as of Tuesday night.The two journalists were part of a group of 40 who were ambushed on Monday in a nature reserve in eastern Burkina Faso near the border with Benin, said Arancha González Laya, Spain’s foreign minister.The authorities in Burkina Faso said in a statement on Tuesday evening that the country had faced “a resurgence of terrorist acts” since Sunday, and that around 10 people had been killed in several attacks.Six people were injured in the ambush on the convoy on Monday, and a Burkinabe soldier was still missing on Tuesday evening. The fate of the others in the convoy, and the identities of those who carried out the killings, were unclear.The eastern parts of Burkina Faso, particularly around the city of Fada-Ngourma, near the reserve where the journalists were abducted, has for several years been a perilous area because of the armed groups operating there.Last year was the deadliest for militant Islamist violence in the region, according to the Africa Center for Strategic Studies, a U.S. Defense Department research institution. About 4,250 people were killed — a 60 percent increase over 2019 — with the Islamic State in the Greater Sahara linked to more than half of the deaths.On Tuesday, the United Nations said a record high of 29 million people were in need of humanitarian assistance and protection in six countries of the region, among them Burkina Faso and Chad, where the killing of the president, Idriss Déby,last week could further destabilize the region.Mr. Déby, who had a poor human rights record, was a key figure in regional efforts to fight off Islamist insurgents in alliance with French and African forces. About 1,200 Chadian troops were deployed this year in the border area between Burkina Faso, Mali and Niger, where Al Qaeda in the Islamic Maghreb has made significant strides.In Burkina Faso, violence has fueled a fast-growing displacement crisis, with more than a million people fleeing their homes since 2019, according to the United Nations’ humanitarian affairs body. Three million people are in need of humanitarian assistance, in a country with a population of 20 million.In addition to violence from militants, Burkina Faso’s military has killed growing numbers of civilians, sometimes in proportions similar to those killed by Islamic insurgents, according to rights groups and analysts. In July, the bodies of at least 180 men thought to have been killed by security forces in the preceding eight months were found in the country, according to witnesses’ testimonies collected by human rights researchers.The two Spanish journalists had histories of working in conflict zones..Mr. Beriain, 43, had reported from Afghanistan, Congo, Iraq and Libya, among other places, according to the regional Spanish newspaper La Voz de Galicia, for which he worked for six years. He also directed a documentary about the nuclear disaster in Fukushima, Japan, and the film he was working on about Burkina Faso was scheduled to air on Movistar, a Spanish television channel.Mr. Fraile, 47, also covered several conflicts and was injured in 2012 while covering the civil war in Syria.The ambush, in the reserve of Pama, occurred near Pendjari National Park, where a guide from Benin and two French tourists were abducted in 2019. The guide, Fiacre Gbédji, was killed, and the two Frenchmen were later rescued, although two French soldiers were killed in a raid to liberate them.Several other foreigners have also been taken hostage in recent years. In 2016, an Australian couple were kidnapped in the north of the country on the day that armed fighters killed dozens of people in the capital, Ouagadougou. In 2018, a Canadian woman and an Italian man were abducted in the country; they were released 15 months later in neighboring Mali. And in 2019, a Spanish Catholic missionary was killed.Raphael Minder and Ruth Maclean contributed reporting.