The Taliban's reclusive leader has said that his fighters have infiltrated the Afghan police and army and were successfully killing a rising number of US-led coalition forces.
Mullah Mohammad Omar emailed his eight-page message to news organisations ahead of the Eid al-Fitr holiday marking the end of the Muslim holy month of Ramadan.
Omar said Afghan security forces were assisting Taliban fighters who infiltrate their ranks, kill foreign troops and then carry their government-issued weapons back to insurgent camps.
"They are able to (safely) enter bases, offices and intelligence centres of the enemy," he said. "Then, they easily carry out decisive and coordinated attacks, inflicting heavy losses on the enemy."
Attacks where Afghan soldiers or policemen, or militants wearing Afghan uniforms, kill their foreign partners is on the rise, but the coalition claims only 10% of the attacks can be linked to infiltrators.
So far this year, 34 foreign troops have been killed in 27 attacks, according to The Associated Press. Last year, 20 international soldiers were killed in 11 such attacks.
White House spokesman Jay Carney said that such attacks were deeply concerning. He said the US-led coalition was continually assessing and refining procedures to ensure the safety of Nato troops. "It is important to remember first of all that our relationship with our Afghan partners is strong and that every day our forces fight alongside Afghan forces," Mr Carney said, adding that international forces partner with about 350,000 Afghan forces on 90% of operations.
The Taliban leader urged Afghan government workers to also switch sides and join the Taliban. The Taliban have set up a new department named "Call and Guidance, Luring and Integration," to help those who leave the government and join the insurgency, he said.
It is a response to the Afghan government's reintegration programme to lure Taliban foot soldiers off the battlefield, help them set up a new life back in their communities and provide development assistance to their villages.
The UN says more than three-quarters of the 1,145 civilian deaths in the first six months of this year were blamed on insurgents.