America's determination to halt illegal immigration across its border with Mexico is set to claim an unusual victim - the jaguar.

The US government has just vetoed a plan to save the species, Panthera onca, one of the world's most endangered, and beautiful, large cats - and activists blame the Bush administration for its determination to cut illegal immigration from Mexico.

'The US is building a wall along the border to keep out immigrants. But that would stop jaguars crossing the border and entering the US. We wanted to set up refuges over here and create breeding populations that might save the species, but the government has said "no way". It doesn't want anything interfering with that wall,' said Kieran Suckling, of the US Centre for Biological Diversity. 'Yet the US is the animals' best hope of avoiding extinction. Its numbers are declining alarmingly today. But now that chance has been blocked - for political reasons.'

Jaguars were once common across the southern United States - as well as in Central and South America - but were wiped out in the US in the sixties. The last animal was shot in 1963. In other countries it has clung on, but numbers have begun to decline dramatically in recent years.

However, conservationists were recently delighted to discover several jaguars had been returning to New Mexico and Arizona from Mexico - probably because global warming was changing their habitat.

Suckling and his colleagues then prepared plans to use these stray jaguars as the core for a breeding population, but have just been told by the US Fish and Wildlife Service their plan will not be adopted. 'The Bush administration doesn't like the idea of reintroducing species and it doesn't want anything getting in the way of its Mexican wall,' he added. 'Our jaguar scheme would have needed gaps in the wall, and that was deemed unacceptable.'

Yet the US, although it killed off its jaguars, is the animals' best chance for survival, say biologists. The US has wild places, is now ecology-conscious, and has organisations that could protect the animal. 'Other countries don't have the resources to save the jaguar. We do and have done so with other species, like the grey wolf, but are now being blocked for political reasons.'