Recruting Americans?

US security sources said they were looking into information from Kenya that residents of Western countries, including the United States, may have been among the militants.

"We do monitor very carefully and have for some time been concerned about efforts by al Shabaab to recruit Americans or US persons to come to Somalia," White House deputy national security adviser Ben Rhodes said, adding he had no direct information that Americans participated.

A spokesman for the British High Commission in Nairobi said:

"We are not going to be drawn into speculation about the identity of the attackers while the investigation is ongoing."

Britain, Kenya's former colonial ruler, has like other nations offered support to help pursue those behind the attack.

US President Barack Obama, whose father was born in the east African nation, offered US help, saying he believed Kenya - the scene of one of al-Qaeda's first major attacks, in 1998, and a neighbor of chaotic Somalia - would continue to be a regional pillar of stability.

Kenyan officials have tried to reassure the country that they are in command of the situation. Officials said there would a news briefing on the situation later on Tuesday.

"We appeal for patience, keep calm, avoid Westgate at all costs and wait for the official communication," the Ministry of Interior and Coordination of National Government in The Office of the President said on Twitter.

Al-Qaeda killed more than 200 people when it bombed the US Embassy in Nairobi in 1998. When fighters from its Somali ideological counterpart stormed the mall on Saturday, they hit a high-profile symbol of Kenya's economic power.

Kenya has sent troops to Somalia as part of an African Union force trying to stabilise the country, which was long without a functioning government, and push back al Shabaab.

Related Stories:

Chinese workers donate blood for Kenya victims

Obama pledges US support after Kenya 'outrage'

China condemns Kenya terror attack

Ambassador consoles victim in Kenya mall attack

Chinese woman among dead in Kenya