Spokesmen for the IMN said on Friday clashes that erupted between police forces and protesters in the capital, Abuja, this week left at least 20 people dead, presstv Reported.
One spokesman said the death toll may be as high as 25.
IMN members regularly take to the streets of the Nigerian capital to call for the release of Sheikh Zakzaky, their leader, who has been in detention since 2015.
Nigerian forces have used live ammunition against the protesters.
The spokesmen said that most of the victims lost their lives after Nigerian troops opened fire on protesters on Monday, adding that four others have since died in police custody of their gunshot wounds.
“More might die in police custody, because there are at least 15 people who are in the detention center with various degrees of bullet wounds, without medication,” one spokesman said.
Sheikh Zakzaky, who is in his mid-60s, lost his left eyesight in a 2015 raid by security forces that left more than 300 of his followers and three of his sons dead. His wife also sustained serious wounds.
The cleric’s son, Mohammad, told Press TV on July 6 that his father was in dire need of medical treatment, as “large and dangerous quantities of lead and cadmium have been found in his blood.”
In 2016, Nigeria’s federal high court ordered Zakzaky’s unconditional release from jail following a trial, but the government has so far refused to set him free.