The head of NATO says Afghan security forces are dying in record numbers because they are leading the fight against the Taliban insurgency.

Figures this week show that more Afghan security forces — army and police — have been killed fighting so far this year than in all of last year with the casualty rate up 6.5 percent. This year 4,634 have been killed in action, compared to 4,350 in 2013.

"The increase in casualties among the Afghan forces reflects that they are now in the lead," said NATO Secretary General Jens Stoltenberg, who is currently visiting Afghanistan.

NATO is set to conclude its combat mission in Afghanistan by the end of the year. Some 12,000 U.S. and NATO troops will remain in a training and support capacity.