Kabul, Afghanistan (CNN) Sometimes you know a war's going badly when your enemy is right in front of you.

About 3 miles outside the southern city of Lashkar Gah, Afghan soldiers can see a white flag. It's not one of surrender -- quite the opposite.

The flag belongs to the Taliban, and shows exactly how close the militant group is to the capital of Helmand province.

Despite Afghan government assurances that the army can hold and retake ground, the strategic province that hundreds of NATO troops -- who have been in the country for the last 15 years -- died fighting for is closer than ever to falling to the Taliban.

Taliban resurgent

JUST WATCHED Afghan troops pull out of Helmand districts Replay More Videos ... MUST WATCH Afghan troops pull out of Helmand districts 02:33

Those inside Lashkar Gah are understandably nervous.

A Helmand police official, who did not want to be named for his own safety, told CNN on Sunday that the army had not made any recent advances, and at least five full districts in the province were already under full Taliban control.

The official said this included the towns of Musa Qala and Nawzad, and that an army offensive to retake the town of Khanisheen was recently repelled by the Taliban.

Lashkar Gah is currently under threat from two directions by the militant group, the official said.

The official confirmed what many analysts had long feared: that the highly valuable opium crop, now being harvested in Helmand, is a key reason for the Taliban's focus on the southern province.

Even a temporary lull in the fighting in Helmand in the past week can be attributed to the Taliban's focus on getting the poppy harvest in, the official said.

Afghan army soldiers patrol in Lashkar Gah, Helmand province.

'It will not fall'

Government representatives strongly reject any suggestion that Helmand is under threat of Taliban control, or that Lashkar Gah would be overrun.

"It will not fall. If it falls, there is no doubt I will resign, but it will not fall," acting Defense Minister Masoom Stanikzai told CNN.

"It is not a rosy picture in Helmand. It's a difficult fight and there are many fighters coming from across the (Pakistan) border, there is no doubt about that."

He blamed the Taliban's recent advances on Pakistani assistance, an oft-repeated charge by Afghan officials.

"Why are we ignoring this fact? Go to Quetta, go to Peshawar. What the hell are those (militant) bases doing there? How are they moving there? How are they communicating there?"

'A bad year'

JUST WATCHED Analyst: Afghan forces can't match Taliban tactics Replay More Videos ... MUST WATCH Analyst: Afghan forces can't match Taliban tactics 03:40

The Afghan army has struggled in Helmand, where U.S. officials were strongly critical of its former leadership in the province.

"2015 was a bad year, but I attribute most of those (failings) to failures of leadership," Maj. Gen. Jeffrey Buchanan, the U.S. forces' deputy chief of staff for operations, told CNN.

He said recently appointed Afghan army leaders were "phenomenal" and that "they still have a very tough set of operations ahead of them, but I disagree completely that Lashkar Gah is on the verge of falling."

As Afghanistan moves into summer, and the warmer months known as the fighting season, existing challenges will be made worse by extreme losses government forces endured nationwide in 2015.

U.S. officials estimate that 5,500 Afghan security force members died that year alone, far more than the 3,500 NATO lost in its entire decadelong campaign.

Deserting to the Taliban

Former Afghan army soldiers have deserted and joined the Taliban.

Death is not the only reason the Afghan army is losing troops: Desertion is rife within the ranks.

CNN met two deserters in Helmand whose stories show the breadth of the problem, who have taken their skills -- months of U.S. taxpayer-funded training -- to the Taliban.

"I did 18 months of army training and took an oath to serve this country," one deserter said. "But the situation changed. The army let us down, so we had to come to the Taliban, who treat us like guests."

The two men still had their old uniforms, army IDs, and even the bank cards they used to withdraw their official wages.

"I decided to leave the army when my dead and injured comrades lay in our base, and nobody took them to hospital. My army training is very useful now, as I am training Taliban fighters with the same knowledge."

Record casualties

More than 3,500 Afghan civilians died last year alone, and another 7,500 were injured -- record figures

The stories of those who have fled to Lashkar Gah provide a snapshot of what Afghans endure daily, often out of the global spotlight.

"My worst memory was how a wedding party was hit by a mortar, killing a large number of women and children," one man said.

"The police left after the fighting intensified and told me to move to a vacant corner of the village. But the bullets and rockets followed, killing 10 people. So I fled here."

Another man came from an area the Taliban now control to buy goods in Lashkar Gah, and described a relative calm in the town of Musa Qala now the Taliban were in control.

"The bazaar is now full of people when it used to be empty. That was because security was bad and some people avoided the government forces in it."

Still, government officials insist they will turn the fight around in Helmand in coming months.

Stanikzai, the acting defense minister, said much of the battle against the insurgency was about reinforcing public perception that the government was winning.

"It is not about the battlefield but the confidence of people in the political future. We have to create it. We have to work on it," he said.

"We have to defend the country."

New recruits attacked

On Monday a suicide bombing attack killed 12 people and injured dozens when a three-wheeled motorcycle loaded with explosives targeted a bus carrying new Afghan army recruits from eastern Afghanistan to Kabul, a spokesman for the Afghan Defense Ministry said.

At least 38 people also were reported wounded in the attack, which happened in Jalalabad, the official said. Jalalabad is the provincial capital of Nangarhar.