Afghanistan's national army and police are slowly maturing, according to the U.S. Army general in charge of training the Afghan forces. Maj. Gen. Robert Durbin says that over the past four years, "steady progress has been made," but "significant challenges" remain.

Durbin says capable and independent Afghan security forces are a prerequisite of a U.S. drawdown in Afghanistan, where a resurgent Taliban has begun to challenge U.S. and allied forces.

A Taliban raid on a joint U.S.-Afghan military facility in the southern city of Kandahar on Wednesday sparked a firefight in which 19 Taliban fighters were killed. There were no reports of coalition casualties.

The U.S. has 23,000 troops in Afghanistan; allied countries including Great Britain contribute another 12,000. Around 3,500 soldiers under Durbin's command are solely dedicated to training native forces, including 30,000 soldiers in the Afghan army and another 60,000 police. All of the Afghan soldiers are fully trained and equipped, according to Durbin, but half of the police lack radios, vehicles and some training.

The Afghan army aims to add 1,000 recruits per month for an eventual total of 70,000. The police force is not adding to its ranks but instead is focusing on improving its existing forces. The Afghan government sets Afghan military manpower goals, Durbin says.

As it expands, the army will add $2 billion worth of equipment donated by the U.S., including body armor, helmets, M-16 rifles and up-armored Humvees. Coalition countries so far have donated 8,000 vehicles to Afghan forces against a requirement for 86,000.

In addition to equipment shortages, the Afghan police struggle with absenteeism and a culture of corruption, Durbin says. But "pay and rank reforms are having desired effects" towards solving those problems.

The army is doing better, according to Durbin. He cites the ongoing offensive Operation Mountain Thrust as the first in which Afghan forces have taken the lead. "The Afghan national army has more troops in this operation than any other country." He says Afghan helicopter crews flying Russian-built choppers flew more than 100 hours supporting the ground troops in recent operations.

Responding to concerns that most Afghan soldiers are illiterate, Durbin says, "Illiterate does not mean stupid".

The general adds that recruitment is no problem. He says security forces could grow faster and beyond current manpower goals, if the Afghan government so desired. And, unlike Iraqi security forces, Afghan forces have not shown any indication of infiltration by religious extremists.

"The greatest challenge," Durbin says, "is that the Afghan national army and Afghan national police face an adaptive enemy bent on destabilizing Afghanistan."