Mahsa Amini: Fighters from Iraq, Lebanon, Syria could be working to suppress Iran protests
Amini, 22, had been detained by morality police who objected to how she was wearing her hijab, and was reportedly beaten into a coma.
The militants described themselves as "the volunteers from Islamic lands" and said they're "willing to give their lives to Ayatollah Khamenei" on social media, according to The Telegraph.
They said they "spontaneously formed" as a group.
Khamenei is Iran's Supreme Leader and is also considered an important religious leader by many Shia Muslims outside Iran.
The fighters are from Shia militia groups under the control of Iran's Revolutionary Guards Corps, the ideological branch of the country's military, according to Iranian opposition groups cited by The Telegraph.
Iran has sponsored a series of Shia militias operating in Arab countries such as Syria, Iraq, and Lebanon in recent years.
The opposition groups added that the militants have been at large-scale demonstrations in Iran before.
Protests over Amini's death have erupted across Iran in recent days, with the first on 17 September.
Authorities have responded with violence and widespread arrests, and at least 41 people have died.
Some women protesters have burned their hijabs. The headscarf is a compulsory item of dress for women who are in public in the Islamic Republic.
Solidarity protests following the death of Amini, whose Kurdish name can be spelled "Jina" or "Zhina", have also taken place in London, Iraqi Kurdistan, Istanbul and beyond.