KABUL, Afghanistan — In one of the most significant coordinated assaults on the government in years, the Taliban have attacked police outposts and government facilities across several districts in northern Helmand Province, sending police and military officials scrambling to shore up defenses and heralding a troubling new chapter as coalition forces prepare to depart.

The attacks have focused on the district of Sangin, historically an insurgent stronghold and one of the deadliest districts in the country for the American and British forces who fought for years to secure it. The Taliban have mounted simultaneous attempts to conquer territory in the neighboring districts of Now Zad, Musa Qala and Kajaki. In the past week, more than 100 members of the Afghan forces and 50 civilians have been killed or wounded in fierce fighting, according to early estimates from local officials.

With a deepening political crisis in Kabul already casting the presidential election and long-term political stability into doubt, the Taliban offensive presents a new worst-case situation for Western officials: an aggressive insurgent push that is seizing territory even before American troops have completed their withdrawal from Afghanistan.

The battle in Helmand is playing out as, about 1,500 miles to the west, Iraq is losing ground to an insurgent force that advanced in the shadow of the American withdrawal there. The fear pulsing through Afghanistan is that it, too, could fall apart after the NATO-led military coalition departs in 2016.