Tajik President Emomali Rahmon has criticized the country's security forces for their "failure" to prevent" the killing of four foreign cyclists in late July.

The attack on a southern mountain road in late July had been prepared for “half a year” and the suspects had been on the police's list of potential terrorists, Rahmon said in Dushanbe on November 10.

Despite that, nothing was done to prevent the attack, the Tajik president said during an event devoted to the Day of Police.

"It was possible to prevent that horrific crime -- look how many gatherings they have held before the attack [and] how many illegal things they did before it -- but we have been negligent," Rahmon said.

The four cyclists -- an American man and woman, a Dutchman, and a Swiss man -- were killed on July 29 when attackers plowed into their group on a road and then stabbed some of them.

Two other foreign cyclists survived the attack, which occurred about 150 kilometers south of Dushanbe.

Days later, Tajik police arrested the alleged ringleader of the group, Hussein Abdusamadov.

The four other men suspected in the attack were killed during a police operation.

Abdusamadov and 14 other Tajiks are currently on trial on suspicion of involvement in the attack.

The extremist group Islamic State (IS) claimed responsibility for the attack shortly after it occurred and released a video showing five men -- at least some of whom appeared to resemble those identified by Tajik officials as suspects killed in a confrontation with security forces -- pledging allegiance to the IS leader.

The Tajik government, however, rejected the claim and instead blamed followers of the Islamic Renaissance Party of Tajikistan (IRPT), a political party that was banned in Tajikistan in 2015.

The leadership of the IRPT -- which served for several years in the Tajik government -- has denied involvement and called the authorities' claims "shameless and illogical slander."