Lagos (Nigeria): At least 800 people died in election-related violence that swept across northern Nigeria, according to international human rights group.

Human Rights Watch said in a statement on Monday that last month's elections in Nigeria "were heralded as among the fairest in the country, but they were also the bloodiest."

Authorities had previously estimated that at least 500 were killed but had hesitated to release an official toll for fear of provoking retaliatory violence.

Protesters in Nigeria's predominantly Muslim north took to the streets as results showed the winner was President Goodluck Jonathan, a Christian from the south.