Gen. Sher Mohammad Karimi and other Afghan officials visit Helmand province’s Sangin district Saturday. The Afghan army has been battling a days-long Taliban offensive in the area. (Watan Yar/European Pressphoto Agency)

— The Taliban has massed hundreds of fighters in Helmand province in its most ambitious attempt this year to seize ground as the U.S. combat mission winds down in Afghanistan, according to Afghan officials.

The fighting has gone on for nearly a week in the southern province, a former Taliban stronghold, demonstrating the insurgency’s ability to mobilize against much improved, but still inexperienced, Afghan security forces.

As of Saturday, the exact toll from the violence remained unclear, but at least several dozen civilians, soldiers and police officers had been killed, Afghan officials said.

“It was a coordinated and organized attack on northern Helmand,” said Omer Zowak, the provincial spokesman. “Afghan security forces have pushed the Taliban back . . . but they are resisting in some parts of Sangin district.”

Sangin, the main target of the Taliban offensive, lies in a valley along the Helmand River where for years insurgents have staged periodic attacks on Afghan and international troops. This week, 45 civilians were killed in Sangin alone and 4,000 were displaced, according to the district’s governor, Sulaiman Shah.

“The Taliban booby-trapped people’s home, putting bombs in front of their houses,” Shah said. “The situation was very bad.”

When U.S. troops began to leave Helmand last year, many American officials predicted that the Taliban would try to dominate the Afghan forces left in charge of Sangin.

For years, the district’s poppy harvest and drug production centers had been a financial boon to insurgents. Over the past two summers, though, the Taliban has appeared to make retaking Sangin a priority.

The past week’s fighting spread to the districts surrounding Sangin, leading to reinforcements being sent to the area. Top Afghan commanders from Kabul flew over the area in helicopters to assess the situation.

The assault appears to be the insurgents’ most effective attempt to date to gain ground in Helmand.

Sediq Sediqi, a spokesman for the Interior Ministry, suggested that more than 1,000 insurgents were involved in the attack. Afghan officials insisted Saturday that the fighting was nearing an end, with troops refusing to cede territory.

“The clearing operation is going on. We’ve killed hundreds of Taliban fighters,” said Gen. Zahir Azimi, a spokesman for the Afghan National Army, who added that the Taliban had failed in its bid to destabilize Helmand.

But the Taliban said its efforts had yielded enormous gains. On its official Web site, the organization claimed to have overrun five government outposts in Sangin.

After the U.S. troop surge began in 2009, thousands of Marines were sent to northern Helmand, where the casualty rate was among the highest in the war.

In March 2011, then-Defense Secretary Robert M. Gates called Sangin “a major strategic breakthrough.”

Security has deteriorated significantly since then. Afghan officials still believe the government’s hold on the district can be sustained, but their confidence is conditional.

“I do believe in the Afghan security forces, but I have a demand for the international community,” said Shah, the district governor. “Before they leave, they should equip our army and police with mortar equipment and strengthen our air force.”