Islamic State released a video on Tuesday purportedly showing attackers pledging allegiance to the militant group before killing four Western tourists in a knife and car-ramming attack in Tajikistan.

The terror group sought to bolster its claim of responsibility for an attack which killed four Western tourists including two Americans on Sunday.

But the Tajik government has accused a banned Islamist opposition party of being behind the attack.

The Islamic Renaissance Party of Tajikistan (IRPT) party's exiled leaders denied any link to the attack and said the authorities were using the incident for political purposes.

Islamic State released a video on Tuesday purportedly showing attackers pledging allegiance to the militant group before killing four Western tourists in Tajikistan

But on Monday, ISIS claimed responsibility for the attack which was originally reported as a hit-and-run road accident.

In a statement, ISIS said that a 'detachment from the soldiers of the Caliphate' had carried out the attack against 'citizens of Crusader coalition countries,' according to intelligence monitor SITE.

On Tuesday, an ISIS outlet published a 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.

This is the moment four Western tourists were killed in a car-ramming and knife attack while on a cycling holiday in Tajikistan

Some of them appear similar to the suspects whose photographs have been published by Tajikistan's interior ministry.

The cyclists were killed on Sunday when a car ploughed 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.

The victims, two Americans, a Swiss and Dutch citizen, were struck by a car while on a popular cycle route in the Danghara district, about 100 kilometres (60 miles) south of the capital Dushanbe.

Another cyclist with the group, a French citizen, escaped without injury and had been questioned by police, he added.

The Dutch foreign ministry said one of the dead tourists was a 56-year-old man who was cycling the route with his 58-year-old partner, without providing names.

The four cyclists were killed when a car ploughed into them on a rural road on Sunday

A Belgian cyclist who said he arrived at the scene after the attack told Flemish broadcaster VRT that he saw 'several cyclists on the ground. Some were completely shocked'.

'When I asked what had happened, the first thing someone said was that they had been hit by a car and that the people who had come out had started stabbing them with knives,' cyclist Nicolas Moerman said.

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.

Four tourists, including two Americans, were killed in Tajikistan by armed attackers in what was originally reported as a hit-and-run road accident. Pictured, the scene after the attack

The attack on Sunday left tourists from the United States, Switzerland and the Netherlands dead and two others injured, the interior ministry said

The dead were on a cycling tour in the impoverished ex-Soviet nation when the car rammed into them. Pictured, the bikes after the attack

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.

Among the dead suspects was 21-year-old Jafariddin Yusufov, the owner of the Daewoo Leganza car that struck the tourists on Sunday afternoon, local officials said.

'(The suspects) had knives and firearms,' said interior minister Ramazon Hamro Rahimzoda, adding that two other cyclists, Swiss and Dutch nationals, were injured and hospitalised.

'One tourist received a knife wound and is being given medical assistance. The victim's condition is stable,' said Rahimzoda, without mentioning a nationality.

In a statement on Tuesday, the interior ministry said it had detained four more suspects and blamed the IRPT for the attack.

The attack took place in the district of Danghara in Tajikistan, 90 miles south of the capital Dushanbe

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.

Jafariddin Yusufov, a suspect in the case and the owner of the Daewoo Leganza that struck the tourists, was killed

'We completely deny the illogical allegation by the interior ministry and condemn this terrorist act,' IRPT leader-in-exile Muhiddin Kabiri told Reuters.

'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.

The Dushanbe government banned the IRPT in 2015, accusing it of plotting a failed coup.

Party leaders who now live in exile have denied the charges and said the move against them aimed to consolidate President Imomali Rakhmon's grip on power.

Earlier on Tuesday, IRPT expressed condolences to the families and nations of the victims and said it hoped the investigation would 'not only refute rumours and assumptions', but also help Tajikistan regain trust in the eyes of foreigners.

Three of those originally on the wanted list and then reported killed included Asomiddin Madzhidov (pictured)