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GHUNDY GHAR, Afghanistan (AP) — The gunfire and explosions echoing across this Taliban-infested district in southern Afghanistan on Friday signaled the end of the opium poppy harvest as militants again turned their attention from agriculture to attacking NATO and Afghan forces.

U.S. Army soldiers perched on this small hilltop base in Kandahar province's Zhari district had a ringside seat to the early morning fighting. It snapped a lull in violence that had lasted almost three weeks while the Taliban focused on taxing the poppy crop, one of its main sources of revenue.

Building up resources is especially important for the Taliban this year as NATO is ramping up its latest military operation in Kandahar, the group's spiritual heartland. Military commanders have characterized the Kandahar mission as the make-or-break battle of the nearly 9-year-old war.

"This is the most gunfire that has happened in weeks," said Staff Sgt. Aaron Christensen, looking down from Strong Point Ghundy Ghar as helicopter gunships pounded Taliban militants who had attacked a U.S. patrol about 1.5 miles (2.5 kilometers) away. "The poppy harvest is definitely over."

Afghanistan produces the raw opium used to make 90 percent of the world's heroin, and the Taliban earn about $300 million per year off the trade, according to the United Nations.

Kandahar itself produced about 16 percent of Afghanistan's opium poppies in 2009, the second-largest amount after neighboring Helmand province. The key districts in Kandahar for poppy are Zhari, Panjwai and Maiwand.

"I really underestimated how much the poppy harvest would impact the Taliban's operations out here," said Capt. Ryan Sheeran, the company commander whose First Platoon is currently based at Ghundy Ghar but also operates in Maiwand. "Taliban operations literally went down to nothing."

That all changed abruptly on Friday. The morning dawned with a roadside bomb attack against Afghan army troops as they traveled along the main highway that runs through Kandahar about a mile (2 kilometers) north of Ghundy Ghar, said Lt. Jonathan Lessman, the commander of First Platoon. The blast triggered an intense firefight that lasted nearly 10 minutes.

About an hour later, militants holed up in a mud compound attacked a U.S. platoon that had set up a temporary observation post east of Ghundy Ghar, Lessman said. Over the next 30 minutes, the soldiers responded with a punishing barrage of grenades and gunfire, while Kiowa helicopters pounded the militants with rockets, sending up clouds of dust and smoke.

It was unclear if there were any casualties from the two incidents.

The U.S. soldiers who were attacked were based at another small outpost in Zhari called Strong Point Lako Khel, which has been a favorite target of Taliban militants because it doesn't enjoy the same defensive hilltop position as Ghundy Ghar.

Both outposts fall under the command of 2nd Battalion, 1st Infantry Regiment, which has responsibility for providing security in western Zhari and Maiwand.

"Now that the harvest is ending, we will definitely see an increase in roadside bombs on the highway and attacks against Afghan and coalition troops," said Lessman.

The Taliban have a strong presence in Maiwand, Zhari and Panjwai, with the latter two districts almost entirely under the militant group's control.

Afghan government efforts to eradicate poppy in the three districts in 2007 and 2008 boosted support for the Taliban from farmers who relied on the militant group to protect their crop.

NATO forces who now patrol the districts have tried to counter that dynamic by telling farmers they will not target their crops but will go after smugglers who take the opium to market — a fine line that is often difficult to walk.

The Taliban have tried to disrupt that message in Zhari and Maiwand, telling farmers that coalition helicopters have been spraying chemicals to destroy this year's poppy crop. The fabrication has gotten some traction because disease and lack of water have reduced this year's harvest by 75 percent compared to 2009, according to farmers.

Lessman, the platoon commander, has tried to counter the Taliban's message as he and his men patrol through poppy fields around Ghundy Ghar that are still dotted with a few workers finishing the harvest. But he is even more focused on keeping his men alert for potential danger.

"The problem with the lull in violence was that it allowed soldiers to get complacent," said Lessman. "Now it's back to business as usual."