Cyclists Lauren Munoz and Jay Austin were tragically attacked and killed on Sunday while riding their bikes through Danghara, a mountainous region in Tajikistan. They were with five other cyclists they’d met during their journey along the Pamir Highway, a bike touring road that cuts through the Pamir mountains of Afghanistan, Uzbekistan, Tajikistan, and Kyrgyzstan, reports Outside Online.

According to NPR, ISIS has claimed responsibility for the attack that claimed four lives. A sedan swerved from the opposite side of the road to hit the cyclists, and witnesses say that the assailants then jumped out of the car and stabbed and killed the two Americans, as well as Markus Hummel, a cyclist from Switzerland, and Rene Wokke, a cyclist from the Netherlands. Three other cyclists survived the attack. The U.S. embassy reports that the ministry of internal affairs detained one suspect and killed at least three others, reports Outside Online.

You can watch a video of the attack below, but be warned, it contains graphic and disturbing footage.

Munoz and Austin started their bike ride in July 2017 in south Africa. They went up to Tanzania, then flew to Morocco and biked through eastern Europe and then through Central Asia. They had planned to go down to Australia and fly to South America, where they would bike back toward the U.S.