By Nick Thorpe BBC reporter in Chisinau, Moldova

An international game of cat and mouse is underway in this apparently sleepy outpost of the former Soviet empire.

The outcome will affect not only progress in conventional disarmament by Russia and Nato, but also evolving East-West co-operation in the international war against terrorism.

At the centre of Western concerns is the east Moldovan district of Trans-Dniestr, which tried to break away from newly independent Moldova in 1991 and has since led a semi-legal existence, unrecognised by the international community and alternately courted and shunned by the government of the day in Chisinau.

Western officials describe it as a ''black-hole'' of lawlessness, where the human rights of the population are systematically denied, and trafficking in weapons, drugs and people is rife.

Trans-Dniestr holds a massive stockpile of 38,000 tonnes of old Soviet military equipment, stored at Colbasna, with some 2,500 remaining troops of the Russian 14th army stationed nearby.

Also of concern is the steel plant at Ribnitsa, which produces weapons for foreign customers whose identities are rarely disclosed.

Treaty timetable

Until December last year, the Russian Federation was proceeding on schedule with planned troop and weapons reductions from Trans-Dniestr and other areas, agreed under the 1990 Conventional Forces in Europe (CFE) treaty, and more recent documents, including the 1999 Istanbul declaration of the Organisation for Security and Co-operation in Europe (OSCE).

About 21,000 tonnes of arms should have been destroyed this year

Under the Istanbul declaration, the remaining 2,500 Russian soldiers should be withdrawn from Trans-Dniestr by the end of this year, with about half the weapons stockpile transported back to Russia and the other half destroyed in situ.

To help that process, the OSCE has agreed to deliver detonation chambers, in which old munitions can be destroyed safely.

But last December, after three train-loads of military equipment were allowed to leave, the Trans-Dniestrian authorities blocked a fourth, and have allowed none out since.

Since January, OSCE officials who have tried to visit the Colbasna weapons dump have been refused access.

By denying us access, we're essentially halted in our abilities to assist the Russians

Major Mike Bruce, of the OSCE weapons destruction programme

And on 13 April, the first detonation chamber, shipped to the port of Odessa in Ukraine and due to be installed at Colbasna, was refused access and diverted instead to Chisinau.

For the past month, it has sat in a well-guarded shed on the edge of the city.

''The current status is that by denying us access, we're essentially halted in our abilities to assist the Russians'', said Major Mike Bruce, of the weapons destruction programme of the OSCE mission in Chisinau. ''We have a lot of equipment in place and are certainly ready to do so at any moment.''

Destruction target

Under the original plan, 21,000 tonnes of munitions, from hand-grenades to 155mm artillery shells, should have been destroyed by the end of the year.

If the Donovan T-10 detonation chamber now waiting in Chisinau, and others waiting to be sent, were installed immediately, more than 13,000 tonnes could still be destroyed this year.

The rest would have to be removed by train, if Russia is to meet its treaty deadline.

Nobody informed (us) that the detonation chamber had been brought to Chisinau

Vyacheslav Sapronov, Trans-Dniestrian official in charge of heavy industry

But for now there is no sign of the Trans-Dniestrian authorities giving way - to the intense frustration of both the OSCE and the Russian Government.

''The issue has not been agreed with us, no documents have been signed and nobody officially informed (Trans-Dniestr's capital) Tiraspol that the detonation chamber had been brought to Chisinau,'' Vyacheslav Sapronov, the Trans-Dniestrian official in charge of heavy industry, said recently.

The OSCE ambassador to Chisinau, David Swartz, replied that it was now up to Russia to persuade Trans-Dniestr to comply.

Mr Sapronov visited Belgium last year at the invitation of the OSCE to see the detonation chamber in action - blowing up old munitions from the First and Second World Wars.

Sanctions threat

A new concern for US officials in the post 11 September world is the possible supply of weapons or weapon components from Trans-Dniestr to so-called ''rogue-states''.

Last week a senior US official in Washington said economic sanctions would be imposed on Moldovan, as well as Chinese and Armenian companies, for allegedly supplying weapons to Iran.

Sources in Chisinau suggest one such company could be the Ribnitsa steel works in Trans-Dniestr. Rocket launchers assembled in Trans-Dniestr are known to have been used in the conflict in Abkhazia in 1993.

The Black Sea ports of Ukraine are within easy reach. As the Donovan detonation chamber was being shipped into Odessa last month, US officials can only guess what was being shipped out of the same port.