Nigerians are demanding answers after activists said "a massacre" of Shia Muslims took place in the country's north over the weekend. 

Local human rights advocates say soldiers killed hundreds in a recent crackdown on Shia leader Ibrahim Zakzaky and his followers in Kaduna state.

Al Jazeera has not been able to verify the death toll, and the Nigerian military acknowledged a "loss of lives" in a statement on Monday, but said it resulted from Shia group members blocking roads.

Both the US government and Amnesty International have called for investigations into the deaths. Iran has also summoned Nigeria's envoy in Tehran, calling the violence "unacceptable."

Many online criticised the Nigerian military and President Buhari's response: