Its claim runs counter to a statement by the Tajik government which accused a banned Islamist opposition party of being behind the attack.
The party’s exiled leaders denied any link to the attack and said the authorities were using the incident for political purposes.
The four cyclists from the United States, Switzerland and the Netherlands were killed on Sunday when a car plowed into them on a rural road. After the crash, the attackers also stabbed their victims, Tajikistan’s interior minister and the US embassy said on Monday.
It was the first known attack of its kind against Western tourists in Tajikistan, a remote ex-Soviet state located north of Afghanistan in towering mountains where Islamists fought an insurgency against a Moscow-backed government in the 1990s.
A purported video of the attack received from an anonymous source and published by Radio Free Europe showed a car doing a U-turn after knocking down the cyclists and driving over several people on a narrow road in broad daylight.
On Tuesday, an Islamic State outlet published a separate video of five men pledging allegiance to its leader Abu Bakr al-Baghdadi. The men, who speak Russian, sit under a black Islamic State flag and refer to each other by Arab names.
Some of them appear similar to the suspects whose photographs have been published by Tajikistan’s interior ministry.
Islamic State, which once controlled large parts of Syria and Iraq, is known to have had some presence in Persian-speaking Tajikistan: a former Tajik elite police force commander defected to the group in 2015.
Security forces killed four suspected attackers on Monday and detained one. In a statement on Tuesday, the interior ministry said it had detained four more suspects and blamed the Islamic Renaissance Party of Tajikistan (IRPT) for the attack.
Citing what it said was the confession of a detained suspect, the ministry said the attackers’ leader had been trained in Iran and the group planned to flee to Afghanistan after the attack.
“We completely deny the illogical allegation by the interior ministry and condemn this terrorist act,” IRPT leader-in-exile Muhiddin Kabiri told Reuters by telephone. “This (statement) draws the attention away from the real criminals.”
The Dushanbe government banned the IRPT in 2015, accusing it of plotting a failed coup. Party leaders now in exile have denied those charges and said the move against them aimed to consolidate the grip of President Imomali Rakhmon, in power since 1992, the second longest-serving leader of an ex-Soviet state.
Kabiri said he was surprised that the government had ignored the claim made by Islamic State.
Iran condemned the attack on Tuesday and rejected the Tajik interior ministry’s allegations.
“The Islamic Republic of Iran strongly denies any link with this incident and existence of any base on its soil for training the assailants,” foreign ministry spokesman Bahram Qasemi was quoted as saying by state news agency IRNA.
Ties between Tehran and Dushanbe have been strained since 2015 when IRPT’s Kabiri, who was already on Tajikistan’s wanted list, appeared at a conference in Iran.