By Nick Childs
BBC Pentagon correspondent
The Pentagon says a number of detainees released from Guantanamo Bay have once again taken up arms against US and coalition forces.
The US says there are risks in releasing prisoners
The US defence department has been saying for some time that it has been receiving such reports.
It says it estimates the number of former prisoners involved at about 10.
Among them, it says, is one man reported to have been behind the kidnapping of two Chinese engineers in Pakistan earlier this month.
According to a Pentagon official another former detainee who was a juvenile when he was first captured and is now a teenager was recaptured while participating in an attack near the Afghan city of Kandahar.
Others have reportedly been killed in other action in Afghanistan.
The United States has been massively criticised for detaining hundreds of prisoners at Guantanamo Bay.
More than 200 have either been released or transferred to the control of their own governments.
What the precise motivations were of those detainees who have returned to fighting is not clear.
All the Pentagon says is that it shows that releasing them is not without risk.