A former leader of the Nigerian militant group Mend has been arrested in connection with two blasts on Friday in Abuja which killed 12 people.
Henry Okah was arrested in South Africa, a spokeswoman for the Nigerian secret police said.
The Movement for the Emancipation of the Niger Delta (Mend), which says it is fighting for a fairer distribution of oil revenue, said it carried the attacks not far from official celebrations of Nigeria's 50th anniversary of independence, and said it had sent a warning shortly before the blasts.
The State Security Service confirmed it had been warned by foreign intelligence services that an attack was imminent.
However, Nigerian President Goodluck Jonathan said "terrorists" not Mend were responsible for the explosions.
And Mr Okah, who leads a faction of Mend, told the BBC on Friday his group was not responsible.
A BBC correspondent says Mr Okah is notorious within Nigeria, known as the gunrunner of Mend, and widely believed to lead a splinter group opposed to the amnesty offered by the government to former fighters last year.
Questions over warnings
British dignitaries who had accepted invitations to the anniversary celebrations withdrew before the event, it has emerged.
The Queen's representative, the Duke of Gloucester, had been due to attend. Former British Prime Minister Gordon Brown cancelled his visit to Nigeria altogether, citing the advice of the British Foreign Office website.
The withdrawals have raised questions about how much the Nigerian authorities knew of impending attacks.
Nigeria's This Day newspaper said British intelligence had warned Nigerian authorities of possible attacks.
A UK Foreign and Commonwealth Office spokesperson confirmed it had "received indications of a heightened security risk" and took immediate action to update travel advice after the Mend warning on Friday morning.
Nigeria's This Day newspaper said British intelligence had warned Nigerian authorities of possible attacks.
The militant group Mend accused officials of acting "irresponsibly by ignoring our forewarning".
