Lagos - Traumatised inmates heard screams and thuds from the gallows as Nigerian authorities on Monday hanged four convicted criminals in the the first known executions in Nigeria since 2006, a human rights lawyer said.
A fifth man who was to be hanged at Benin City Prison was saved when the executioner had technical problems with the gallows, Chino Obiagwu of the national lawyers' rights group LEPAD told The Associated Press in a telephone interview.
Amnesty International said the man, identified as Thankgod Ebhos by Obiagwu, is at "imminent risk of execution".
The London-based organisation's deputy Africa director, Lucy Freeman, said the hangings would mark "a truly dark day for human rights".
Attorney General Henry Idahagbon of Edo State confirmed the executions, the News Agency of Nigeria reported.
Obiagwu said the men were hanged despite pending suits at the appeal court and had been on death row for 16 years. He said two were his clients, convicted of murder, but he did not know for what crimes the others had been sentenced.
"Under Nigerian laws, an appeal and application for stay of execution should restrain further action ... By executing the prisoners, Nigeria's government has demonstrated a gross disregard to the rule of law and respect for the judicial process," he said.
He feared the fifth man would be hanged on Tuesday unless great pressure was immediately brought on the government.
Amnesty International said more than 1 000 people are reportedly on death row in Nigeria.
Obiagwu said a court dismissed his organisation's appeal challenging the state government's signing of execution warrants and a motion to stop executions. That was around 15:00.
"They [authorities] had already started preparing for the executions, they turned us away from the prison and by 18:15. We heard from clients [in the prison] that they had been executed."
He said traumatised inmates called him to describe "terrible sounds" like a drum rolling, shackles scratching and the screams of those condemned begging for mercy.
"The death row prisoners in the suit contend that to execute them after over 16 years of trauma, suspense and imminent death would amount to cruel, inhuman and degrading treatment," Obiagwu said.
He identified those hanged as Chima Ejiofor, Daniel Nsofor, Osarenmwinda Aiguokhan and Richard Igagu.
LEPAD has taken legal action to prevent executions since all Nigeria's state governors said in March 2011 they wanted to resume them. A suit was filed on behalf of all death row inmates.