The United States has admitted it will never be able to clean up all the unexploded weapons that lie around the Panama Canal.

The US military is due to hand the Panama Canal zone back to the Panamanian government by 31 December 1999.

Ever since it occupied the zone 90 years ago, the US has used large areas of the land around the canal as shooting ranges.

The US and Panamanian governments both agreed the importance of military training to defend what is one of the world's most strategically and economically important strips of land.

'Clean-up impossible without irreversible damage to area' say the generals

Under the 1977 Torrijos-Carter treaty, signed by US President Jimmy Carter, the US is obliged to take all practicable measures to get rid of the unexploded ordnance that littered the region, including chemical weapons.

That is not a problem in most of the territory, but the US military now says at least 3,000 hectares of dense jungle will be fenced and declared off-limits.

The army's argument is that it is simply too difficult to clear this area without damaging the environment.

That is an excuse that many Panamanians and US environmentalists are having trouble accepting.

They have accused the Pentagon of exaggerating the technical problems to avoid paying for a thorough but expensive clean-up.