Nigeria's Okah on trial in South Africa for Abuja bombs
The trial has opened in South Africa of a former leader of Nigerian oil militants over bombings at Nigeria's 50th independence celebrations in 2010.
Henry Okah denied the 13 charges related to acts of terrorism.
He was arrested in Johannesburg a day after two car bombs in the Nigerian capital Abuja killed at least 12 people.
The Mend militant group, of which he was a senior leader, claimed responsibility for the attacks.
Attacks in the Niger Delta, the oil-producing region of Nigeria, have declined since a 2009 amnesty for militants ended years of conflict.
Godsday Orubebe, Nigeria's minister of the Niger Delta, told the court in Johannesburg that Mr Okah was a "key figure in the Niger Delta struggle and the militants had a lot of respect for him", AFP news agency reports.
Mr Okah is being tried under laws that stipulate that South Africa is obliged to try him as he has been a resident in the country and now has South African citizenship.
"Based on the information we have and how we are approaching this case we are confident that we will get a positive conviction," South Africa's National Prosecution Authority spokesperson Phindile Louw told the BBC.
He has been in custody in South Africa ever since his arrest in October 2010 and his lawyers say they want to make a fresh application for bail.
The BBC's Will Ross in Lagos says Mr Okah is a controversial figure in Nigeria.
The son of a naval officer from the Niger Delta, he became a very senior member of the Movement for the Emancipation of the Niger Delta (Mend), which severely disrupted the country's oil operations, he says.
Mend said it was fighting against injustice and exploitation.
Mr Okah was arrested on gun-running charges in Angola in 2007 and then transferred to Nigeria but never convicted.
He was released after two years under the amnesty for oil militants and he returned to South Africa, where he had lived since 2003.
His faction of Mend has never fully participated in the amnesty process.