Authorities have identified four cyclists who were killed while riding in Tajikistan in an attack that has been claimed by the IS terror group.

The victims had all kept online blogs documenting their intercontinental bike journeys.

A couple from Washington DC who quit their jobs to cycle and had already toured three continents were among those killed in Sunday's attack.

The other two were a Swiss citizen and a Dutch national.

American couple Lauren Geoghegan and Jay Austin, both 29, had been travelling for over a year.

In April, Mr Austin wrote during a bike tour of Morocco: "Badness exists, sure, but even that's quite rare.

"By and large, humans are kind. Self-interested sometimes, myopic sometimes, but kind.

"Generous and wonderful and kind. No greater revelation has come from our journey than this."

The pair had cycled through Africa and Europe before flying to Kazakhstan in May.

The reason for this low-budget journey was simple, Mr Austin wrote.

"Life is short and the world is big and we want to make the most out of our youth and good health before they're gone."

Ms Geoghegan's parents released a statement praising their daughter's "enthusiastic embrace of life's opportunities, her openness to new people and places, and her quest for a better understanding of the world".

On Sunday they were killed when a car drove into a group of seven foreign cyclists outside the Tajik capital, Dushanbe.

Three other cyclists were injured by the attackers, who jumped from the car and stabbed the cyclists with knives after the crash.

On Monday, the so-called Islamic State group released a video purporting to show the attackers pledging allegiance to the group's leader.

The tourists were attacked while riding on the Pamir Highway, a Soviet-era road that stretches 1,200 miles (2,000km) near the border with Afghanistan.

Slain Swiss cyclist Markus Hummel described the trip along the Silk Road from Xi'an in China to Kyrgyzstan on his blog as "a dream come true", according to AFP.

"Since we are already on the road, we definitely don't want to miss the Pamir Highway in Tajikistan," he and his travel partner - who was injured in the attack - wrote.

Rene Wokke, a 56-year-old Dutch cyclist, has also been identified as among the dead.

His partner, Kim Postma, a 58-year-old hospital administrator, was injured in the incident.

The pair, from Amsterdam, had left Thailand in February and planned to arrive in Tehran in September before flying back to the Netherlands.