The Afghan army is waging its largest-ever solo offensive against the Taliban, hoping to strike a decisive blow ahead of the spring fighting season and prove it can rout the insurgents without the aid of U.S. and NATO combat troops.

Afghan troops have been slowly pushing up through a fertile river valley in the southern Helmand province, with special forces mounting nighttime helicopter raids into mud brick compounds and ground troops gradually advancing across the poppy fields that in past years have furnished the insurgents' main cash crop.

U.S. and British troops suffered some of their biggest losses of the decade-long war here, seizing territory that was later lost by ill-equipped and poorly trained Afghan forces. Afghan President Ashraf Ghani has vowed to break the grim cycle, and the latest offensive is widely seen as a test for his efforts to overhaul the army and police since taking office in September.

Ghani was personally involved in planning the operation, which is codenamed Zolfiqar — meaning double-edged sword — and which began on Feb. 10, according to Maj. Gen. Kurt Fuller, deputy chief of staff for U.S. and NATO operations in Afghanistan. Ghani heads to Washington later this month, where he is expected to seek enhanced U.S. military backup, particularly air support.

"This is an incredibly important operation," said a Western diplomat who spoke on condition of anonymity in order to discuss the secret operation. "This is Ghani's attempt to demonstrate to the U.S. and the U.S. Congress that Afghan ground forces are able to take the lead and conduct offensive operations if they have the right enablers to support them."

U.S. and Afghan officials say local security forces are so far proving they can take the fight to the Taliban without the aid of foreign combat troops. There are 13,000 foreign soldiers in the country, down from a peak of 140,000 in 2009-2010, with 5,000 U.S. troops engaged in counterterrorism operations against the Taliban and al-Qaida.

U.S. military leaders have advised the troops in Helmand and helped plan the operation, but American troops are not involved in the fighting.

Fuller said the troops have already cleared large areas where the insurgents had been entrenched for more than a decade, saying the Taliban's casualties were higher than those of government forces by "a factor of 10 to one."

He said Afghan forces had found bunkers, tunnels, trench lines, and a giant slingshot apparently used to fling grenades at government forces.

He said the Sangin district, which had seen months of heavy fighting, was declared clear on Friday, adding that Afghan forces had "met with heavy resistance that was more than they anticipated."

Gen. Mohammad Salim Ahses, the head of the national police, told The Associated Press by telephone from Sangin that 385 Taliban fighters had been killed there, including 31 commanders. It was not possible to confirm those figures. The areas where the fighting is taking place are not accessible to journalists, and few Afghan officials were willing to speak about the operation.

The international charity Emergency said its hospitals in Lashkar Gah, Helmand's capital, and the national capital Kabul had seen casualties almost double in February to 226 over the same month last year due to increased insurgent violence across the country, according to program coordinator Luca Radaelli.

"We are definitely seeing a spike in the number of war casualties coming in from the operation in Helmand," he said, adding that most were men and many were policemen. Further details on the casualties, including a breakdown of dead and wounded on each side, were not immediately available.

The real test will come later, when Afghan forces try to hold hard-won territory.

Fuller said Afghan officials have begun meeting with local leaders to plan the building of new schools, clinics, police stations and courthouses. He said tribal elders are already helping to recruit residents for the local police and border guard.

Helmand's deputy governor, Mohammad Jan Rasoolyar, said small army and police posts, each of which will house 100 men, are being built across the valley. "This time we are moving according to a proper plan" to keep the Taliban from returning, he said. "We will not leave this place alone."

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Associated Press correspondents Mirwais Khan in Lashkar Gah, Afghanistan, and Rahim Faiez and Amir Shah in Kabul, Afghanistan, contributed to this story.

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