U.S. authorities are urgently looking into information given by the Kenyan government that foreigners were among armed militants who attacked a Nairobi shopping mall over the weekend, killing at least 62 people, U.S. security sources said.
Kenyan security forces are still continuing an operation to secure the Westgate Mall and free any remaining hostages, meaning conclusive evidence proving the involvement of foreigners is not yet available.
However, a national security source said that the United States had been notified through official channels that Kenyan authorities now believed that foreigners, likely including U.S. citizens or residents, were among the gunmen who attacked the mall.
Reuters earlier on Monday quoted Julius Karangi, Kenya's chief of general staff, saying that the attackers included gunmen from several countries. "We have an idea who they are, their nationality and even the number," Karangi said.
He added: "We also have an idea this is not a local event. We are fighting global terrorism here and we have sufficient intel (intelligence) to suggest that." Karangi said the attackers were "clearly a multinational collection from all over the world."
The U.S. national security source said that Kenyan authorities had passed similar information to American authorities but that it was still unclear how much hard evidence the Kenyans had.
A European security source said that Western authorities still had reason to be wary of claims by Kenyan officials of foreign involvement in the attacks.
U.S. officials had been looking for evidence that U.S. citizens or residents were involved in the attack at least since Sunday, when a Twitter account purporting to represent the Somalia-based militant group al Shabaab published what it said were the names of three Americans, a Canadian, a Swede, two Britons, and a Finn who participated in the attack.
Multiple U.S. security sources said U.S. investigators now believe the Twitter account and its claims were bogus.
However, U.S. authorities acknowledged that over the past several years, as many as several dozen Americans have traveled to Somalia to train or fight with al Shabaab, many of them from Somali exile communities in Minneapolis-St Paul, Minnesota.
Some Shabaab militants recently claimed that Omar Hammami - an Alabama man who traveled to Somalia, joined al Shabaab, and made YouTube rap videos promoting the group - had recently been killed after falling out with the group's leadership.
A U.S. official said that the claims about Hammami's violent demise were regarded in Washington as credible.