In the last two years, almost 9,000 Afghan Army soldiers and policemen have been killed in fighting with the Taliban as they have assumed the lead for security in Afghanistan, U.S. military officials said today.

And that high fatality rate for Afghanistan's security forces is not sustainable, a senior U.S. commander said.

Lieutenant Gen. Joseph Anderson told reporters today that 8,984 Afghan Army soldiers and policemen have been killed in action the past two years.

The 4,634 Afghan security personnel killed in action in 2014 was a 6.5 percent increase over the 4,350 killed last year. But Anderson said NATO officials had actually expected the Afghan fatality rates to have been "much higher based on the role they've played and where they've been."

Army Lost Nearly $420M-Worth of Equipment in Afghanistan

Detainee Brought From Afghanistan to US for Trial

Afghan Officials Walk Away From Colorado Training

Overall the Afghan security forces "are winning" in their fight against the Taliban, Anderson said, but noted the casualty rate is "not sustainable." The Afghan Army currently has 156,000 soldiers in its ranks and the police forces number 155,000.

Officials have acknowledged that Afghan military fatalities have risen significantly as Afghan forces took the lead for security from U.S. and NATO troops, but never to this level of specificity. Anderson could not provide statistics prior to 2013 to show how much the fatality numbers have gone up.

For comparison, 4,478 U.S. military service members died in the war in Iraq and 2,210 Americans have died in Iraq since 2001.

Afghan security officials are working to boost their recruiting to deal with the high casualty rates and attrition rates, Anderson said.

The Afghan police is working to change tactics and procedures to better protect their forces in the field against roadside bombs. Afghan police forces are believed to make up the bulk of the casualties as they are less well trained and equipped than Army units and are frequently the target of Taliban attacks.

"They do need to decrease their casualty rate," said Anderson, noting that improving their medical evacuation capabilities could help bring down the number of fatalities. Afghan forces are currently carrying out 88 percent of all medical and casualty evacuations in Afghanistan through a combination of air and ground transportation.

"All those things have to continue to improve to reduce those numbers because those numbers are not sustainable in the long term," Anderson said.

The force of 20,000 American troops currently in Afghanistan is scheduled to be reduced to 9,800 by year's end. The remaining U.S. forces will focus on advising and assisting the Afghan military, though about 1,000 of them will still conduct counter-terrorism missions, U.S. officials said.