A suicide car bomb targeting Western troops near a US-run NATO military base in the Afghan capital Kabul wounded at least three foreign soldiers and three civilians on Friday, police said.
The attack came a week ahead of the inauguration of President Hamid Karzai for a second term and as US President Barack Obama mulls advice on sending more troops to fight the Taliban.
"Around 7:45 am (0315 GMT) a suicide attack committed by a white Corolla car targeted a coalition forces vehicle on the Jalalabad-Kabul Road," said Abdul Ghasar Aayedzada, criminal police investigation chief for Kabul police.
The targeted vehicle was heading towards Camp Phoenix, he said.
"Three foreign soldiers have been injured, they are possibly American," he told reporters on the scene.
Three civilians were also wounded, although their injuries were not serious, the police official added.
The blast took place near Camp Phonenix, a centre of training programmes for Afghan army and police. It is run by US forces, although also has some presence from NATO member countries.
"It was a suicide attack near Camp Phoenix," said Zemaray Bashari, spokesman for the Afghan interior ministry.
A spokesman for NATO, which together with the US military maintains more than 100,000 troops in Afghanistan, confirmed an explosion near the base.
"There was an explosion. We don't know what it was, but there was an explosion outside Camp Phoenix," said Sergeant First Class Kevin Bell.
Investigations had begun, he said.
NATO and US-led troops in Afghanistan have put training of Afghanistan's security forces at the heart of efforts to hand over responsibility for fighting a Taliban insurgency, at its deadliest since the 2001 US-led invasion.
Camp Phoenix occasionally comes under attack, mostly from rocket and mortar fire.
The website of Combined Joint Task Force Phoenix says troops at the base train the Afghan army and police.
It is led primarily by US Army National Guard. As of September this year there were more than 1,700 national guardsmen there.