Lagos, Nigeria (CNN) -- Three people have been arrested in Nigeria and are being questioned in connection with the Friday blasts that killed 12 and injured 50 in the nation's capital, a spokesman for President Goodluck Jonathan said Saturday.

The Movement for the Emancipation of the Niger Delta, known as MEND, claimed responsibility for the attack in Abuja and said Saturday it had given the Nigerian government advance warning.

"The irresponsible attitude of the government security forces is to blame for the loss of lives," MEND said in a Saturday statement.

The group reported it had warned Nigerian security forces five days prior to the attack.

"The security forces were also warned one full hour to the first bomb blast ahead of the general alert sent to the media and told to steer the public from all parked cars which was not done," the statement continued.

The attack came as the West African country celebrated 50 years of independence.

The International Committee of the Red Cross appealed for blood donations to assist the wounded.

Nigerian President Goodluck Jonathan later called the action a terror attack that was designed to "disrupt" the anniversary, said presidential spokesman Imo Niboro. But he said it had nothing to do with Niger Delta issues or MEND.

MEND, which represents militants in the oil-rich Niger Delta, is an umbrella organization of several rebel groups. It has been battling the government for years over fairer distribution of the country's oil wealth.

MEND said Henry Okah, who many say is an influential member of the group, had been harassed by authorities in South Africa, where he lives.

"Okah has never been involved in any MEND operations but has always been blamed for every attack which is strange to us," MEND's statement said.

"They (Nigerian security forces) were given 5 days prior notice (about the attack) which led to the harassment of Henry Okah on Thursday, September 30 in South Africa," the group said.