( CNN ) -- A suicide bomber attacked a U.S. Embassy convoy in Kabul on Monday morning along a busy highway that is part of the route to Bagram Air Base, east of the capital, an embassy spokesman told CNN.
"There were several injuries, including one American who was evacuated and is being treated at this time," said Joe Mellott, a U.S. Embassy spokesman. "We have had reports that some innocent Afghan bystanders were injured or possibly killed."
In their accounts of the incident, Kabul police and Western sources said at least three people died in the attack that they said hit a U.N. vehicle.
"The whole area has been sealed off by NATO ISAF (International Security Assistance Force) troops," CNN's Nic Robertson reported. "They've sealed off a very large section of the road."
Robertson said it is not uncommon for suicide bombers to target international convoys along the route, known as Jalalabad Road.
Last month, a suicide bomber attacked the entrance to Bagram Air Base -- the nerve center of military coalition operations in Afghanistan -- during a visit by U.S. Vice President Dick Cheney, killing up to 23 people and wounding 20 more.