KABUL - A suicide bomb blast struck near a US military base in the Afghan capital on Friday, officials said.

"It was a suicide attack near Camp Phoenix," said Zemaray Bashari, spokesman for the Afghan interior ministry.

"We have no information on who it was targeted against and no information on casualties," he told AFP.

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.

Bashari said the area had been cordoned off by police.

Camp Phoenix, on the outskirts of Kabul, is run by US forces, with some NATO member nations maintaining a presence there.

It is also a base for the Afghan army, which is being trained by international forces in the hope it can take over the responsibility for fighting the Taliban insurgency.

The camp occasionally comes under attack, mostly from rocket and mortar fire, though without casualties.

The website of Combined Joint Task Force Phoenix says the base trains and mentors the Afghan National 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.