The United States army has said it will not be able to clear away all the military waste left behind in the Panama canal zone.

After ninety years of occupation, the Americans are due to return the bases they still hold in the zone to the Panamanian government by the end of this year.

Under the terms of a treaty, they must take all practicable measures to dispose of unexploded ammunition, including chemical weapons.

But the United States military now says large areas of dense jungle will be fenced off and declared off limits, as it's too difficult to clear without damaging the environment.

Campaigners have accused Washington of exaggerating the technical problems to avoid the expense of cleaning up the zone. .