The seven cyclists were apparently run over by a man in a car who then fled. A group of men armed with firearms and knives then killed four cyclists and wounded three others.
A Swiss man was killed in the attack and a Swiss woman was hospitalized with severe knife wounds, according to a report in Swiss news portal 20 Minutes.
A 56-year-old Dutch citizen and two US citizens were also killed in the attack. Nicolas Moerman, a cyclist who arrived at the scene soon after, told a Flemish news station: "I asked what had happened and the first thing someone said was that they had been hit by a car and that the people who had come out had started to stab them with knives."
The attack occurred in the region of Danghara, approximately 150 kilometres southeast of the Central Asian nation's capital Dushanbe.
The route, which runs not only through the desert but also at attitudes of more than 4,000 metres, is popular with intrepid cyclists.
The Tajik government attributed the attack to the opposition Islamic extremist Islamic Renaissance Party of Tajikistan. Islamic State (IS), however, has also claimed responsibility.
The attack had originally been deemed an accident by the Tajik Ministry of the Interior, according to a statement published on July 29th.
A subsequent communiqué said the car involved had been recovered in the village of Torbulok in the Danghara District. Tajik police have apparently identified the culprits and detained them. Two resisted and were killed, according to that statement.
Tajik news sources claimed five suspects, all trained in Iran, had been killed in subsequent operations.
The Swiss Federal Department of Foreign Affairs is providing consular services to the Swiss survivor.