The casualties were caused after police started shooting at dozens of supporters of Islamic Movement in Nigeria (IMN), who took part in a religious procession to celebrate the birth anniversary of Prophet Muhammad in Zaria town of northern Kaduna State.
Local media reports quoting witnesses said police assaulted participants in an unprovoked attack and randomly opened fire at them.
IMN holds annual processions on the anniversary in an effort to lay the ground for stronger unity and solidarity among Muslims and provide solutions for their problems.
Nigeria has been cracking down on the IMN for several years.
Sheikh Zakzaky has been in detention since December 2015 after his home in Zaria was brutally raided by Nigerian forces, during which he was beaten and lost his left eye.
During the violent crackdown, three of his sons lost their lives, his wife sustained serious wounds and more than 300 of his followers were killed.
IMN members regularly take to the streets of the Nigerian capital Abuja and several other cities to call for the release of Sheikh Zakzaky.
Londoners decry human rights abuses in Nigeria
Meanwhile, a number of organizations concerned about the deteriorating human rights situation in Nigeria were set to hold a demonstration in London on Thursday.
The London-based the Islamic Human Rights Commission (IHRC) would urge the international community to hold Nigerian President Buhari accountable for the ongoing persecution of the IMN and its leaders.
The demonstrators were to call on Buhari to abide by court orders, stop killing innocent people and release those who are being unlawfully detained.
Since the 2015 massacre, Nigerian authorities have regularly targeted peaceful marches, religious gatherings and properties associated with the IMN, often with fatal consequences and with total impunity.
IHRC has also repeatedly expressed concern over the deteriorating health conditions of Sheikh Zakzaky.
In a letter to the United Nations earlier this year, dozens of Western intellectuals called on UN chief Antonio Guterres to pressure Nigeria into releasing the senior Muslim figure.
They also urged the world body to take concrete action against ongoing violations being committed against scholars and rights campaigners by Nigerian authorities and the administration of President Buhari.
In July, Zakzaky’s son, Mohammad, said after visiting him that he was shocked by his father’s worsening medical condition. Mohammad said large and dangerous quantities of lead and cadmium had been found in Zakzaky's blood and the cleric needed to be immediately hospitalized.
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.