At least 13 protesters were killed during mass protests in Nigeria against the country's economic crisis that turned violent in several states, a rights group said Friday.

Authorities confirmed four people killed by a bomb and the arrests of hundreds in the protests that triggered curfews in several states.

Amnesty International's Nigeria director Isa Sanusi said in an interview that it independently verified the deaths that were reported by witnesses, families of the victims and lawyers.

More than 300 protesters were arrested and curfews imposed in the northern states of Kano and Katsina after the looting of government and public properties, Nigerian police said. One police officer was also killed and several others injured.

The protests were mainly over food shortages and alleged bad governance in the country. Nigeria's public officials, frequently accused of corruption, are among the best paid in Africa, a stark contrast in a country that has some of the world's poorest and hungriest people, despite being one of the continent's top oil producers.

Carrying placards, bells and Nigeria's green-and-white flag, protesters chanted songs as they listed their demands, including the reinstatement of gas and electricity subsidies whose removal as part of the government's audacious reforms to grow the economy has had a knock-on effect on the price of just about everything else.