Traditional African rulers whose ancestors collaborated with European and Arab slave traders should follow Britain and the United States by publicly saying sorry, according to human rights organisations.

The Civil Rights Congress of Nigeria has written to tribal chiefs saying: "We cannot continue to blame the white men, as Africans, particularly the traditional rulers, are not blameless."

The appeal has reopened a sensitive debate over the part some chiefs played in helping to capture their fellow Africans and sell them into bondage as part of the transatlantic slave trade.

The congress argued that the ancestors of the chiefs had helped to raid and kidnap defenceless communities and traded them to Europeans. They should now apologise to "put a final seal to the history of slave trade", it said.

"In view of the fact that the Americans and Europe have accepted the cruelty of their roles and have forcefully apologised, it would be logical, reasonable and humbling if African traditional rulers ... [can] accept blame and formally apologise to the descendants of the victims of their collaborative and exploitative slave trade."

Estimates vary that between 10 million and 28 million Africans were sent to the Americas and sold into slavery between 1450 and the early 19th century.

More than a million are believed to have died in transit across the so-called "middle passage" of the Atlantic due to inhumane conditions aboard slave ships and the brutal crushing of any resistance.

Three years ago Tony Blair described Britain's participation as a "crime against humanity" and expressed his "deep sorrow". The US Senate voted for an apology this year.

Shehu Sani, head of the congress, said it was calling for traditional rulers to apologise now because they were seeking inclusion in a forthcoming constitutional amendment in Nigeria.

"We felt that for them to have the moral standing to be part of our constitutional arrangement there are some historical issues for them to address," he told the BBC World Service. "One part of which is the involvement of their institutions in the slave trade."

He said that on behalf of the buyers of slaves, the ancestors of the traditional rulers "raided communities and kidnapped people, shipping them away across the Sahara or across the Atlantic".

Many slaves captured inland in Africa died on the long journey to the coast.

The position was endorsed by Henry Bonsu, a British-born broadcaster of Ghanaian descent who examined the issue in Ghana for a radio documentary. He said some chiefs had accepted responsibility and sought atonement by visiting Liverpool and the United States.

"I interviewed a chief who acknowledged there was collaboration and that without that involvement we wouldn't have seen human trafficking on an industrial scale," said Bonsu, the co-founder of digital station Colourful Radio.

"An apology in Nigeria might be helpful because the chiefs did some terrible things and abetted a major crime."

The non-government organisation Africa Human Right Heritage, based in Accra, Ghana, supports the campaign for an apology. Baffour Anning, its chief executive, said: "I certainly agree with the Nigeria Civil Rights Congress that the traditional leaders should render an apology for their role in the inhuman slavery administration." He said it would accord with the UN's position on human rights.

But the issue was not a high priority for most African citizens, according to Bonsu. "In my experience it's mainly the African diaspora who want an apology. People aren't milling around Lagos or Accra moaning about why chiefs don't apologise. They are more concerned about the everyday and why they still have bad governance."

Fred Swaniker, the founder of the African Leadership Academy, said: "I'm not sure whether an apology is needed, but it would be worth looking at and acknowledging the role Africa did play in the slave trade. Someone had to find the slaves and bring them before the Europeans."

The shameful history of some traditional leaders remains an awkward subject on which many politicians prefer to maintain silence. One exception was in 1998 when Yoweri Museveni, the president of Uganda, told an audience including Bill Clinton: "African chiefs were the ones waging war on each other and capturing their own people and selling them. If anyone should apologise it should be the African chiefs. We still have those traitors here even today."