Armed police are searching for gunmen inside this shopping mall in the Kenyan capital, Nairobi.

At least 20 people were killed here on Saturday after gunmen opened fire.

Sporadic gunfire continued at least two hours after the attack began.

Earlier, scores of shoppers were led to safety by police, some in shock, others injured.

The local Red Cross says more casualties are inside the Westgate shopping complex.

Witnesses say they heard grenade blasts.

Others say they saw several armed assailants storm the shopping mall.

It looked like an attack, they say, not a robbery.

The militant group al Shabaab in neighboring Somalia - which is linked to al Qaeda -- has threatened in the past to strike this very mall.

It's popular with Nairobi's ex-pat community, and it would have been packed with shoppers on a Saturday morning.

But there was no immediate reaction from al Shabaab and no official statement, either, from police about the attac