"We know that he is being interrogated by security agents in South Africa, and that this comes as no surprise ... on Thursday, Henry's Okah's house in South Africa was raided by operatives from Interpol," Ndege said.
"And the allegation then was that he was plotting to bomb Abuja on Independence Day. Of course, this actually happened on Friday."
Nigeria's State Security Service admitted on Saturday that it had received a warning that there was an attack planned during the independence day celebrations.
"Unfortunately, there's no way security can be 100 per cent foolproof," Marilyn Ogar, the State Security Service spokeswoman, told The Associated Press news agency.
"We are happy all the same that the event went on smoothly and it wasn't interrupted."
The secret service said had stepped up security after the warnings, including towing 65 vehicles from the streets and cordoning off roads leading to the parade ground.
Mend issued a warning to journalists about an hour before the attacks, telling people to stay away from festivities at Eagle Square in Abuja. It criticised the government for doing nothing to end the poverty in the delta despite the billions of dollars it receives in oil revenue.
"Several explosive devices have been successfully planted in and around the venue by our operatives working inside the government security services," the email, signed by Jomo Gbomo, said.
The group has said it gave security services five days notice of the plan to attack the celebrations.
Goodluck Jonathan, Nigeria's president, who himself in from the oil-rich region in the south, acknowledged that "security lapses" had allowed the bombing to happen, but did not saw whether he had any plans to overhaul the security agencies.
Nigeria's This Day newspaper, citing presidency sources, reported that UK intelligence services had also uncovered information about a possible plot and passed on a warning to Abuja. The Duke of Gloucester, who was due to represent Queen Elizabeth at the event, pulled out.
Mend has been fighting for years for a greater share of oil revenues for the delta, home to Africa's biggest oil and gas industry, but signed an amnesty with the government last year.
Source: Al Jazeera and agencies