Police commissioner Mathew Iteere told reporters it was too early to determine the cause of the blast. He said blackened wires inside the trading centre indicated a possible electrical fault and ruled out a grenade attack.
Two shopkeepers told Reuters independently that they saw a man drop a bag inside the trading centre moments before the blast.
“He came into the shop twice, looking at T-shirts. He said he didn’t have money so he left. Then he came back,” said Irene Wachira. “[He was] three shops away from where I was. He left a bag and a few moments later we had an explosion. The roof caved in and debris started falling on us,” Wachira said.
Prime Minister Raila Odinga said Kenyans would not be cowed by “terrorists”.
More than 10 people have been killed in a string of attacks in Nairobi and the port city of Mombasa since Kenya sent troops into Somalia in October to fight al-Qaeda-linked militants.
Nairobi has blamed the al-Shabab militants, who merged with al-Qaeda earlier this year, for the surge in violence and kidnappings that has threatened tourism in East Africa’s biggest economy and wider regional destabilisation.
A spokesperson for Kenya Power, the country’s sole electricity distributor, said initial investigations had ruled out any electrical malfunction.
A military helicopter hovered in the skies above downtown Nairobi and the security forces cordoned off nearby streets.
Dense black smoke billowed from a fire inside the badly damaged building and sirens blared as emergency service crews rushed to Moi Avenue, a major road running through the city centre.
Medics applied bandages to the walking wounded gathered by nearby buildings and some bystanders wailed in shock. Clothing, shoes and blown out windows littered the road.
Crowds carried away people seen with blood streaming down their faces. Iteere said 28 people had been wounded.
In the days after Kenya deployed soldiers across the border, al-Shabab warned Nairobi to withdraw from its southern strongholds or risk bringing the “flames of war” into Kenya.
In April, the US embassy in Kenya warned of a possible strike on Nairobi’s hotels and key government buildings, which it said was in the last stages of planning.
The recent attacks have tended to target low profile institutions such as bars and nightclubs, where security is typically relatively light.
“Maybe it is these al-Qaeda people. They are wasting life for nothing. Just innocent people going about their business,” said Wilfred Kimani who was several blocks away when the blast occurred.
Outside Nairobi’s Jamia mosque, one Somali refugee who identified herself as Aisha said she feared a backlash if al-Shabab or its sympathisers were behind the explosion.
“It’s bad because Kenyans may get angrier now.”
There have also been several attacks near the border with Somalia since Kenya’s military incursion. At least five people were killed in two separate attacks in the remote region on Saturday.
Currency traders said the blast weakened the Kenyan shilling At 1230 GMT the local currency traded at 85.55/75 against the dollar after earlier trading at 85.30/50.
“We have seen a bit of depreciation on the local currency. It’s right in the central business district, so it’s not very good news to be getting and I think that causes some fear,” said Duncan Kinuthia, head of trading at Commercial Bank of Africa. – Reuters