More than 1,000 Afghan soldiers died in action this year, the highest since the Taliban insurgency began, as the army assumes more responsibility before NATO forces withdraw in 2014, officials said Sunday.

"In the past nine months, 906 Afghan army soldiers were killed. A total of 1,056 soldiers were killed in 2012," defence ministry spokesman General Mohammad Zahir Azimi told reporters in Kabul.

"The toll has increased compared to the previous years."

The ability of the rapidly-expanding army to thwart the Islamist insurgency is key to Afghanistan avoiding civil war as about 100,000 international troops head home.

Azimi said the army had now taken the lead role for security in more than 75 percent of the country, though he added that it needed better equipment and protection against land mines to cut fatalities.

NATO is aiming to train up 350,000 Afghan soldiers and police by the end of 2014 to ensure stability in Afghanistan, but challenges remain in the transition process.

Desertions, poor re-enlistment rates and low morale are among the key problems troubling Afghan and NATO commanders.

So-called "insider" attacks by Afghan security forces on their NATO colleagues and mentors have left more than 60 foreign troops dead this year, seriously undermining trust between the two forces.

The Taliban were ousted from power in 2001, but have waged an 11-year insurgency against the US-backed government of President Hamid Karzai.