Afghan soldiers stand guard Tuesday following weeks of heavy clashes to recapture territory from Taliban militants in Baghlan province, north of Kabul. (Massoud Hossaini/AP)

As NATO’s secretary general was meeting with Afghan leaders here Tuesday, Taliban fighters were seizing further territory in southern Afghanistan during a bloody fight with Afghan troops.

The NATO chief, Jens Stoltenberg, praised Afghan security forces during a news conference with President Ashraf Ghani, but the loss in Helmand province was a blow to the government’s troubled efforts against the insurgency.

The Khanashin district in Helmand fell to the Taliban after insurgents had “amassed” in the area “for days,” a local official said. Police and army personnel abandoned their posts outside government buildings after hours of fighting, another security official in Helmand said. Neither official was authorized to speak to the media. Both sides suffered casualties, the officials said.

Police and army spokesmen told Afghan media late Tuesday that the withdrawal from Khanashin had been a “tactical retreat” but that they were still battling with insurgents and the Taliban did not yet control the area.

Still, the Taliban’s apparent gains in the district — a windswept patch of desert about 100 miles from Helmand’s provincial capital, Lashkar Gah — comes just weeks after government forces withdrew from two other districts in the province, effectively ceding control to insurgents.

Late last month, Afghan army and police personnel pulled out of Helmand’s Musa Qala and Now Zad districts following months of deadly battles with the Taliban. The two areas had alternated between government and Taliban control over the past year, and Afghan security forces suffered from heavy casualties, desertions and low morale, local officials said.

The pullout has raised concerns about the security forces’ ability to hold on to key territory, particularly ahead of the traditional fighting season that takes place in the warmer months. The Taliban-led insurgency has expanded since foreign troops left the country in 2014 and as Afghans have become increasingly fed up with a government seen as weak and corrupt. The fighting has contributed to the highest number of civilian deaths since the United Nations began tracking casualties in 2009.

Helmand has long been an insurgent hub and a center of Afghanistan’s opium industry, much of which is controlled by the Taliban, with opium sold at bazaars across the province. The United States has deployed hundreds of Special Operations forces to assist Afghan forces there in recent months, and in January, Staff Sgt. Matthew McClintock was killed in a Taliban attack in the province.

But most foreign troops have gone home. Stoltenberg said Afghan forces, after taking “full charge of security across the country, ” had made “great progress in the fight against terrorism.”

However, according to a report from the Afghanistan Research and Evaluation Unit, a local think tank, as soon as NATO advisers left the low- and mid-level army ranks, the Afghan National Army “began showing signs of decay.”

“Security is bad all over Helmand, and no progress has been made by Afghan forces,” said Namatullah Ghafari, a lawmaker from Helmand.

“They suffer from weak leadership,” he said. “And the people in Helmand are worried.”

Khanashin briefly fell to Taliban insurgents in December but was swiftly recaptured by government forces. Similar pitched battles have been taking place across Helmand for months, including in Marja, once a showcase for U.S. counterinsurgency operations in Afghanistan.

“The Afghan forces in Marja right now have only one option: to fight for their lives,” said a tribal elder from the area who requested anonymity so he could speak openly about security failures in the province.

“They can’t flee. The Taliban controls the supply routes to these forces,” he said, adding that the government “only controls about 5 percent of the district.”

Stoltenberg said Tuesday that NATO will continue to support Afghan forces but that the organization’s troops “would not go back to a combat operation.”

“We will continue to provide financial support so they can be sustainable in the long term,” he said. “The single most important thing we want to see is that Afghanistan continue to implement reforms.”

The United States alone has spent more than $60 billion training and equipping Afghan security forces, according to the Office of the Special Inspector General for Afghanistan Reconstruction, a U.S. government watchdog.

“I expect 2016 to be difficult,” Stoltenberg said.

Mohammad Sharif and Sayed Salahuddin contributed to this report.

Stretched by its fight against Taliban, Afghan army raises recruitment age

Commando-style assault on Afghan jail frees scores of Taliban inmates

Afghan forces straining to keep the expanding Taliban at bay