By Crispin Thorold BBC correspondent in Kabul

The eruption of violence in northern Afghanistan is a graphic reminder of the challenges facing the Afghan interim administration and the international community.

Nato-led peacekeepers only operate in Kabul

Afghanistan is a patchwork of instability.

Large factions compete in the north, remnants of the Taleban launch almost daily attacks in the south, and drug related violence racks much of the country.

As Nato defence ministers discuss Afghanistan in Colorado Springs, many within the country believe a much more radical peacekeeping solution, than those on the table, is needed, if a return to the anarchy of the 1990s is to be stopped.

At the moment the Nato-led international peacekeeping force (Isaf) only operates in the capital, Kabul.

PRT solution

Various options to extend the peacekeeping mandate are being explored, all of which initially focus on securing provincial towns across Afghanistan.

US forces have stepped up its offensive against Taleban remnants

Most are based on the model of the Provincial Reconstruction Teams (PRT) - groups of soldiers and development workers based in provincial towns.

Four PRTs have been established by coalition troops.

American forces run a PRT in Gardez and Kunduz, the British are operating in Mazar-e-Sharif, and soldiers from New Zealand have recently taken over a PRT in Bamiyan.

In theory, the advantage of the PRTs is that they are area-specific.

They can bring some security to a district and they allow development agencies to respond to the particular needs of a region.

'A sledgehammer for a pin'

However, in practice PRTs are small and have to operate within very limited guidelines.

Karzai is struggling to impose his rule among feuding warlords

Their restricted mandate means PRT soldiers cannot get involved in green-on-green fighting (factional clashes), they cannot intervene if they see human rights abuses and they cannot stop drugs production.

In other words, they are under-resourced and under-mandated. The recent factional violence near Mazar-e-Sharif is a case in point.

Even if their rules of engagement allowed, what could 72 British army soldiers do to prevent hundreds of militiamen clashing?

Nato diplomats are reported to have asked the United Nations Security Council to approve a plan in which the German army will take over the US-run PRT in Kunduz.

Some reports suggest up to 450 soldiers will be sent to the city.

"A sledgehammer for a pin," in the words of one aid worker.

Kunduz is relatively safe and stable, while half of Afghanistan's provinces are considered high-risk by agencies working there.

Why, ask critics, is the focus on Kunduz, when the main southern city Kandahar is a hotbed for militancy?

Why not secure the main urban centres, they say? Herat, Kandahar, Qalat, Ghazni, Mazar-e-Sharif and Shibargan.

'Poppy tax'

If some semblance of stability could be brought to these, then mobile patrols could be established on the circular road that loops around the country, linking them.

The main cities need stability

From there, so the theory goes, the seven main roads to neighbouring countries could also be secured, allowing trade to flow more freely.

All of this is a best-case scenario.

Many observers fear that not enough troops will be provided to secure even Afghanistan's main towns, and even if thousands of soldiers were committed, the country would be far from stable.

In the south and east, remnants of the Taleban launch almost daily attacks, many in rural areas.

Drug production creates "ambient insecurity" across the country. Regional militias, which control opium-producing areas, charge a "poppy tax".

'No easy fixes'

This hugely lucrative business causes factional violence across the country, not on the scale of the violence near Mazar-e-Sharif, but significant all the same.

The recent clashes in the north are a timely reminder that two years after the US-led war against the Taleban, Afghanistan is once again sliding towards the chaos.

There are no easy fixes.

Each area has its own particular problems, which peacekeeping forces alone will not solve, but little development work can be done in such an unstable environment.