Masked gunmen stormed a packed upmarket shopping mall in Nairobi Saturday, spraying gunfire and killing at least 20 people and wounding dozens more before holing themselves up in the complex.
The attackers were "pinned down" after hours of painstaking evacuations, with police going shop-to-shop to secure the Westgate shopping mall, a security source told AFP.
"The attackers have been isolated and are pinned down in an area on one of the floors. The rest of the mall seems to be secure," a security source told AFP at the scene.
Senior police sources said they believed a well-organised "terror gang" of about 10 people was behind the assault on the shopping centre, which is popular with wealthy Kenyans and expatriates and was packed with around 1,000 shoppers when it was besieged at midday.
An eyewitness told AFP that he heard the gunmen speaking Arabic or Somali and saw the group executing shoppers, in what appeared to be the worst attack in Nairobi since an Al-Qaeda bombing at the US embassy killed more than 200 in 1998.
The Kenyan government, which has troops battling Islamist Shebab insurgents in neighbouring Somalia, said it was still too early to say who was responsible.
"Investigations have begun to find out the perpetrators of this crime. I urge Kenyans not to speculate," Interior Minister Joseph Ole Lenku said in a statement.
The Red Cross said that some 20 people had been killed and another 50 wounded in the attack.
Police at the scene said a suspect wounded in the firefight had been detained and taken to hospital under armed guard.
"This cannot be a normal robbery because all the survivors are saying how the group confronted them and opened fire," a senior police official told AFP on condition he remained anonymous.
"We have reports there were up to 10 or so attackers and they appeared to be wearing a similar outfit, and others covered their faces," another police official said. "The pattern of the attack and the way they were speaking to their targets clearly point to a well-planned attack by a terror gang."
As security forces worked to secure a multi-screen cinema complex on the mall's top floor, a police source said it had been confirmed that the attackers were holding at least seven hostages. As darkness fell over Nairobi, their fate was unclear.
Kenyan troops could be seen moving around and inside the shopping centre while special forces had joined the operation.
An AFP reporter said she saw at least 20 people rescued from a toy shop. Dozens of wounded, some of them bleeding children, were stretchered away from the mall.
'I saw people being executed'
A shop manager who managed to escape said at one point "it seemed that the shooters had taken control of all the mall".
"They spoke something that seemed like Arabic or Somali," said a man who escaped the mall and gave his name only as Jay. "I saw people being executed after being asked to say something."
Shocked people -- black, white and Indian -- could be seen running away from the Westgate centre clutching children while others crawled along walls to avoid stray bullets.
Kenneth Kerich, who was shopping when the attack happened, described scenes of panic.
"I suddenly heard gunshots and saw everyone running around so we lied down. I saw two people who were lying down and bleeding, I think they were hit by bullets," he said.
"Initially we thought it is police fighting thugs. But we could not leave until when officers walked in, shot in the air and told us to get out."
An eyewitness who survived the assault by gunmen said he saw the body of a child being wheeled out of the mall.
"The gunmen tried to fire at my head but missed. At least 50 people were shot. There are definitely many casualties," mall employee Sudjar Singh told AFP.
"I saw a young boy carried out on a shopping cart, it looked like he was about 5 or 6. It looked like he was gone, he was not moving or making any noise."
Vehicles riddled with bullet holes were left abandoned in front of the mall as the Red Cross appealed for blood donations and police instructed residents of the Westlands neighbourhood to stay away.
The four-storey mall, which has several Israeli-owned businesses, is a hub for Nairobi-based Westerners and one of the foremost symbols of Kenya's affluent classes, It has long been considered a potential terror target. It opened in 2007 and has restaurants, cafes, banks, a large supermarket and a cinema.
It is popular with the large expatriate community living in the residential neighbourhoods around it, including with foreign staff from the United Nations, which has its third largest global centre nearby.
Security agencies have regularly included the Westgate shopping centre on lists of sites they feared could be targeted by Al Qaeda-linked groups.
The Somali insurgents from the Shebab group have repeatedly threatened to strike at the heart of Kenya in retaliation for Nairobi's military involvement alongside the government they are trying to overthrow.
British Foreign Secretary William Hague said on Twitter that his country was "in close touch with Kenyan authorities about the attack in Nairobi, our urgent priority is the welfare of UK nationals."