Abuja, Nigeria (CNN) -- A militant group said it carried out the car bombing that rippled through Nigeria's capital Abuja Friday, a blast that killed eight people and wounded 21 others.
Two bombs exploded at almost the same time outside the Justice Ministry as the West African nation marked 50 years of independence, according to an International Red Cross official.
The death toll is expected to rise, the Red Cross official said.
The Movement for the Emancipation of the Niger Delta later claimed responsibility for the attack in the capital. MEND, the key 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 is claiming responsibility for the attack," the group said in an e-mail to CNN.
The city was "very calm" later Friday, according to Nigerian Information Minister Dora Akunyili.
"Whatever happened, we are able to have a very successful celebration," Akunyili said.
The Red Cross said at least 38 vehicles were destroyed by the blasts.
President Goodluck Jonathan was at the main event in Abuja, where he inspected a guard of honor as police scoured the scene for clues.
The site of the explosions was about 0.6 miles (1 kilometer) from Eagle Square, where the president was attending the event, Ajukwu said.
U.S. Embassy officials in Abuja issued an alert warning Americans to either remain home or go to a safe location. It applied to American citizens nationwide.
The explosions struck not long after a rebel group warned crowds earlier Friday to evacuate the venues of the event.
Earlier, MEND said it had planted "explosive devices" and told anniversary day attendees to stay away from vehicles and trash cans.
"There is nothing worth celebrating after 50 years of failure," the rebel group said in a statement.
"For 50 years, the people of the Niger Delta have had their land and resources stolen from them. The constitution before independence which offered resource control was mutilated by illegal military governments and this injustice is yet to be addressed."
CNN's Christian Purefoy, Isha Sesay, Faith Karimi and Joe Sterling contributed to this report.