Dozens of death row prisoners in Nigeria have not been able to appeal their sentences, others have waited up to 24 years to have their appeals heard, and some are just teenagers, Amnesty International said Tuesday.

At least 80 of the 736 inmates currently languishing on death row in Africa's biggest oil producer were sentenced by tribunals, without the right to appeal their sentences, the London-based rights group said. Others have faced decades-long delays for appeals, due to a lack of legal representation or missing case files, it said.

In addition, there are at least 40 juvenile offenders on Nigeria's death row. Their ages at the time of their alleged crimes ranged from 13 to 17 years old.

The rights group called upon the Nigerian government to declare a moratorium on executions, saying the West African nation's criminal justice system is "riddled with corruption, negligence and a nearly criminal lack of resources."

Government officials had no immediate comment on the Amnesty report.

The report also claimed that thorough, impartial police investigations into capital crimes were rare and said over half of the death row inmates were convicted on the basis of written confessions that many said were extracted under torture.

"It is truly horrifying to think of how many innocent people may have been executed and may still be executed," said Aster van Kregten, Amnesty International's Nigeria researcher.

Nigeria made an attempt to address the flaws by establishing two commissions of inquiry, which both recommended a moratorium on death sentences because the existing justice system could not guarantee a fair trial, but no action has been taken yet.

The report says Nigeria's soaring violent crime rate puts pressure on police to make fast arrests and few politicians want to publicly oppose death sentences.

"The death penalty is used as a distraction from the real issue: Addressing the underlying factors that lead to violent crime," the report said.

Nigeria is Africa's most populous nation, with 140 million people. In spite of massive oil earnings, poverty is widespread and criminality and corruption are major problems.