Policemen walk towards burnt vehicles at the scene of a blast at a business district in Abuja June 25, 2014. At least 21 people were killed when a suspected bomb tore through the crowded shopping district in the Nigerian capital Abuja during rush hour on Wednesday, police said, adding to the toll of thousands killed in attacks this year. [Photo/Agencies]

ABUJA - At least 21 people were killed when a suspected bomb tore through a crowded shopping district in the Nigerian capital Abuja during rush hour on Wednesday, police said, adding to the toll of thousands killed in attacks this year.

It was not immediately clear who was responsible for the blast and no one claimed responsibility. However, militant Islamist group Boko Haram has increasingly targeted civilians in its bloody five-year insurgency.

The suspected bomb would be Abuja's third in three months and comes as the Nigerian government and military face rising public anger over their inability to protect citizens from daily gun and bomb attacks across Africa's most populous country.

The explosion rocked a crowded district near the popular Banex Plaza shopping centre in the upscale Wuse 2 neighbourhood just before 4 pm (1500 GMT).

"After a preliminary investigation, we can confirm that 21 people were killed and 17 injured," police spokesman Frank Mba told reporters at the scene, adding that one suspect had been arrested.

Another suspect was killed by soldiers as he tried to escape on a motorcycle, the spokesman for Nigeria's National Information Centre said.

Witnesses said the blast shattered windows, sent smoke billowing into the air and carved out a large crater.

One local man, Shuaibu Baba, was in a shop making photocopies when the blast hit, killing his taxi driver who was waiting for him outside.

"I lost a driver. And why? Because I came to photocopy for 10 naira ($0.06) a page," he said.

"I begged him to take me here and this is the end."

Officials said the explosion hit while the district was at its busiest, packed with shoppers and rush-hour commuters.

"I heard a loud blast, it shattered the windows of the shop. We ran out. A lot of people ran too, some with bloodstains," said Gimbya Jafaru, who was shopping nearby.