Authorities in Afghanistan say a suicide bomber drove his explosives-laden car into a convoy of U.S. and Afghan forces in the southern city of Kandahar early Wednesday.
Local officials say at least three people were killed and four others were wounded.
A U.S. military spokesman Colonel Jerry O'Hara says there were no immediate reports of American casualties.
Afghan and U.S. forces have cordoned off the site of the blast in downtown Kandahar - a former stronghold of the ousted Taleban regime.
Taleban insurgents and their allies have recently stepped up attacks, mostly in eastern and southern Afghanistan.
One American soldier and a German member of the NATO-led international peacekeeping force were killed in separate attacks in eastern Afghanistan and Kabul this week.
Some information for this report provided by AP, AFP and Reuters.