The Islamic State (IS) group has released a video purporting to show a group of men who killed four foreign cyclists in Tajikistan on Sunday pledging allegiance to its cause.
Earlier authorities had blamed a banned Islamist party, citing an alleged confession of one arrested suspect.
Two Americans, a Swiss and a Dutch national were hit by a car in Danghara, south-east of the capital Dushanbe.
The attackers then stabbed their victims.
Two other foreigners were injured.
Earlier on Tuesday, Tajikistan's interior ministry said that a man suspected of leading the attack was an active member of the Islamic Renaissance Party of Tajikistan (IRPT), which was outlawed three years ago.
Exiled leaders of the IRPT denied any link to the attack, saying the authorities were trying to use the incident for political purposes, Reuters reports.
Tajikistan's government banned the IRPT in 2015, accusing it of planning a coup.
The video released by IS shows five young men seated under a tree in a mountainous area with the IS flag in the background, BBC Monitoring reports.
One denounces the rulers of Tajikistan as "apostates", who "sold their religion" and allowed the country to be occupied by "unbelievers".
They later join hands and swear loyalty to IS leader Abu Bakr al-Baghdadi, before pledging to attack "unbelievers".
The identity of the men and whether it was they who carried out the attack cannot as yet be verified.
IS efforts in Central Asia
By Mina Al-Lami, BBC Monitoring
IS isn't known to have a presence in Tajikistan. However, the group has had members from the country, and from other Central Asian states. Tajik authorities have in the past arrested alleged IS recruiters or sympathisers.
In May 2015, a former member of Tajikistan's special OMON police unit, Gulmurod Khalimov, pledged allegiance to IS and migrated to territory held by the group. This was flaunted in an IS-linked video in an effort to inspire others in Tajikistan to follow his example.
In February 2018, IS said its attacks in Russia and former Soviet countries had entered a new phase, inciting sympathisers to attack Christians in "the Caucasus, Crimea, and Central Asia countries".
"The current stage", said IS via its weekly newspaper al-Naba, "does not require groups with big numbers of trained fighters, nor heavy weapons. Rather, it requires a mujahid to use whatever weapon he can get his hands on" to attack.
Such attacks, it said, would instil fear in Christians and prompt them to leave these countries.
Following Monday's attack, four suspects were killed by authorities in a special operation, the interior ministry said.
Another four were arrested, and a damaged car believed to have been involved was recovered.
An amateur video which appears to be of the attack captures the moment a car is driven into unsuspecting cyclists.
According to Tajikistan's interior minister, three of the tourists died instantly and one on the way to a nearby hospital.
"One had knife wounds, he received medical help, now his condition is stable," Ramazon Hamro Rahimzoda told reporters.
The victims were on a tour in the Central Asian country with three other tourists from France, the Netherlands and Switzerland.
Tajikistan has struggled with poverty and instability since the former Soviet republic became independent in 1991. It had declared 2018 a "year of tourism", AFP news agency said.