(CNN) The number of Afghan security personnel, who are tasked with defending the war-ravaged country from a continuing insurgency, has dropped by 10% in a year, a strong indication that a multi-billion dollar training program funded by the US is failing.

The rare insight into the condition of Afghan security personnel comes in the latest report on the conflict by the US inspector general, who is tasked with assessing its cost to the US taxpayer.

In its quarterly report for the US Congress, the Special Inspector General for Afghan Reconstruction (SIGAR) says it was told by the US military that the total number of Afghan security personnel, including police and military, stood at 296,409 in January this year. A year earlier, the figure was 35,999 higher, the SIGAR report says. "These figures represent a sharp decline in strength from the same period last year," the report notes.

No immediate explanation was provided for the change, although the growth of the insurgency in Afghanistan in the past year will likely have led to the deaths of many police or army personnel, or contributed to the decision of others to leave the forces.

It is hard to know for sure -- while the SIGAR report notes the total number of security personnel from year to year, the inspector general is not allowed to disclose the number of Afghan soldiers and police who have died, been wounded or are just not turning up to work.

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