KABUL, Afghanistan — As Afghan forces struggle to break a weeklong Taliban siege of central neighborhoods in the provincial capital of Kunduz, insurgents are also stepping up pressure on urban centers in western and southern Afghanistan, officials said Sunday.

In Farah Province, in the west, Afghan security forces have called for reinforcements to hold the line against the insurgents’ offensive. Fierce battles are also raging around Lashkar Gah, the capital of Helmand Province, in the south, which has been surrounded for months as Afghan forces have failed to reverse Taliban gains.

The fall of central areas of Kunduz City, where street-to-street fighting has displaced tens of thousands of people, has punctured the belief that Afghan forces, trained and financed by Western allies, could protect major urban centers. In recent months, Afghan troops have suffered record casualties.

Still, Afghan and Western officials say, the inexperienced Afghan forces, operating largely on their own now that the NATO mission has drawn down to an advisory role, have so far held their own despite being stretched to defend several areas simultaneously.