The Iranian government has summoned the Tajik ambassador to Tehran to protest allegations linking Iran to an attack that killed four foreign cyclists in Tajikistan.

The Iranian Foreign Ministry said in a statement that it summoned Ambassador Nematullo Emomzoda on August 1 to convey Iran's "strong" protest over "false and unfounded" claims made by the Tajik government.

The attack on a group of foreign cyclists on a remote mountain road on July 29 claimed the lives of two Americans, a Dutchman, and a Swiss citizen. Three other foreigners -- one Dutch, one Swiss, and one French -- were injured.

The Islamic State (IS) has released a video of what it said were the attackers pledging allegiance to the extremist organization.

However, the Tajik Interior Ministry on July 31 accused the banned Islamic Renaissance Party of Tajikistan (IRPT) of being behind an attack. The group denied the allegation as "baseless and irrational."

The ministry also said that the attackers were led by an "active member" of the IRPT who "underwent training in Iran."

The authorities offered no immediate proof of the claims.

Iranian officials told the Tajik envoy in Tehran that showing "indifference" to and "tolerance" of Sunni extremists would undermine peace, stability, and security in the region, Foreign Ministry spokesman Bahram Qasemi said on August 1.

Human rights groups have condemned Tajikistan's treatment of the IRPT, which was branded a "terrorist organization" and banned in 2015 after the government accused it of plotting a failed coup. Relations with Tehran are tense.