A purported video of the incident published online by Radio Free Europe showed a car doing a U-turn on a narrow road after it had already knocked down a group of cyclists and then running over a few of them.
A "wanted" notice disseminated by Tajik authorities named two suspects aged 18 and 19 from the same village close to the Tajik-Afghan border, and a third one, 21, from the town of Nurek located not far from the site of the attack.
The US Embassy said it could not name the two American victims due to privacy concerns, but indicated that it also considered the incident to be an intentional attack.
"We strongly condemn the cruelty of the attackers and recognise that they in no way represent the kindness and hospitality of the Tajik people," it said in a statement.
Switzerland's Foreign Ministry confirmed the death of one Swiss national and said it was in contact with the second tourist, who has been injured.
New Zealand's Ministry of Foreign Affairs warns travellers to consider their need to visit the country. The Ministry has warned against all but essential travel in regions bordering Afghanistan, Uzbekistan and Kyrgyzstan "due to criminal activity and the presence of landmines and we advise against all tourist and other non-essential travel to these areas."
Caution is advised for New Zealand visitors to the rest of the country, citing on their website safetravel.govt.nz that "Tajik security forces reportedly prevented 12 terrorist attacks during the course of 2017. New Zealanders are advised to monitor the media for information."
Tajikistan country profile
Tajikistan is a mountainous ex-Soviet state bordered by Afghanistan, China, Kyrgyzstan and Uzbekistan. It remains one of the poorest countries in the former Soviet sphere.
languages: Tajik and Russian
Population: 8,742,000
Source: UNDP