An explosion has hit a crowded shopping centre in Nigeria's capital Abuja, killing at least 22 people and wounding dozens of others, officials said.

Wednesday's blast hit Emab Plaza just as people were getting ready to watch Nigeria play Argentina in the World Cup on the many TV sets for sale inside.

Witnesses told Al Jazeera they saw body parts scattered around the entrance of the mall.

Parts of the building and many cars parked outside were completely destroyed by the impact of the explosion. 

It was not clear what caused the blast but suspicion fell on the armed group Boko Haram, which has attacked Abuja twice in the last 10 weeks. A car bombing in April killed 75 people at the Nyanya bus terminal on the city's outskirts, and a similar bombing at the same spot on May 1 left 19 people dead.

Al Jazeera's Yvonne Ndege, reporting from Abuja, said an investigation had been launched into the cause of the latest explosion and that security was being beefed up across the capital.

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"Nigeria's security services insist they are winning the war against Boko Haram. But say these kinds of attacks are difficult to stop," she said. 

Wednesday's explosion came just two days after police blamed Boko Haram for a blast that struck a medical college in the northern Nigerian city of Kano, killing at least eight people.

Boko Haram, which aims to create a state in northern Nigeria ruled by Islamic law, did not immediately claim responsibility but the school matched its target of Western education.

The group, which has attracted international condemnation since April when it kidnapped more than 200 schoolgirls who remain captive, has also been blamed for abucting 60 girls and women and 31 boys from villages in northeast Nigeria over a three-day period - Thursday, Friday and Saturday.

On Saturday, scores of Boko Haram fighters attacked four other villages close to Chibok, in Borno state, near the Cameroon border, from where hundreds of girls were kidnapped in April.

Witnesses said at least 33 villagers were killed as well as six vigilantes and about two dozen Boko Haram fighters.

Source: Al Jazeera and agencies