EU foreign policy chiefs got a first-hand look on Thursday at Russia's Baltic enclave Kaliningrad, a thorn in the side of EU enlargement plans, amid renewed fears of a nuclear build-up in the province.

Kaliningrad - known as Koenigsberg until the Soviet Union changed its name in 1946 - has historically been the realm of Teutonic knights, Prussian kings and, after 1933, Nazi soldiers.

Today, the city of Kaliningrad and its surrounding region are part of Russia, but completely cut off from it.

All land routes to Russia cross the territory of what were once Soviet republics, but are now independent states.

Kaliningrad was renowned throughout the Soviet Union for some of the more monstrous examples of Soviet architecture.

And that is causing big problems for Russia, since those states want to join Nato and the European Union.

As Nato expands to include Poland and possibly Lithuania - Kaliningrad's two direct neighbours - the enclave risks becoming completely isolated.

Kaliningrad's neighbours - Poland and Lithuania - will be forced to improve border security and introduce visa requirements with the Kaliningrad region.

That could mean big difficulties for the shuttle traders who travel visa-free to and from Poland, and who help keep the region's economy afloat.

Kaliningrad was a major military base during the Cold War. It retains many characteristics of a military base, even if the military presence has been greatly reduced.

It is a tense area. Russia has been complaining that Nato reconnaissance flights near Kaliningrad have become more frequent.

And the West is worried about recent reports - strongly denied by Moscow but which may now have been backed up with satellite images - of tactical nuclear weapons, redeployed by Russia in the Kaliningrad region.

Kaliningrad was renowned throughout the Soviet Union for some of the more monstrous examples of Soviet architecture.

But the end of the USSR brought hard times.

Drug abuse is so widespread it has helped make Kaliningrad region the Aids capital of Russia

The economy came near total collapse. Kaliningrad was declared a "free economic zone" in 1992 in the hope of attracting foreign investment.

But with the zig-zag economic policies pursued in Russia, the free economic zone was abolished in 1995. It was reinstated two years later - still without bringing real results.

Liberal politicians in Moscow have come up with the idea of turning the Kaliningrad region into a new Hong Kong, by setting up an off-shore zone.

Once proud Kaliningrad has become grim

Some radical Russian politicians have even suggested selling the Kaliningrad region in exchange for writing-off Russia's debt to Germany. But Moscow does not seem ready to relinquish control.

Kaliningrad's westward-looking neighbours are worried.

The region is plagued by organised, violent crime - often with political motives. Drug abuse is so widespread it has helped make the region the Aids capital of Russia.

This prospect of having a poverty-stricken, crime-ridden outpost of their eastern neighbour on their doorstep is not one which Warsaw or Vilnius find attractive.