Critics are protesting a US border patrol plan to poison vegetation along a 1.1-mile stretch of the Rio Grande riverbank in Texas to eliminate dense foliage used as hiding places by illegal immigrants and smugglers.

Some opponents of the action compare it to the Vietnam war-era Agent Orange chemical spraying programme.

The $2.1m (£1.4m) pilot project is due to begin this week. If successful, it could be expanded along as much as 130 miles of river in the patrol's Laredo sector, as well as other parts of the US-Mexico border.

Opponents are concerned that the spraying will occur near the cities of Laredo and Nuevo Laredo, Mexico.

"We don't believe that is even moral," said Jay Johnson-Castro Sr, executive director of the Rio Grande International Study Centre, located at Laredo Community College, adjacent to the planned test area. "It is unprecedented that they'd do it in a populated area."

US border patrol and Environmental Protection Agency officials say the herbicide planned for the test is safe for animals. The programme is intended to keep border patrol agents safe and make their jobs easier.

"We are trying to improve our mobility and visibility up and down the river," said border patrol agent Roque Sarinana.

Members of the Laredo city council have raised concerns and called on Mexican president Felipe Calderon to intervene. Mexican officials are worried that the herbicide imazapyr could threaten the Nuevo Laredo water supply.

Imazapyr was registered in the US in 1984. The EPA concluded after tests that "there is a reasonable certainty that no harm will result to the general population, and to infants and children from aggregate exposure to imazapyr residues".

A US government outline of the project indicates the border patrol is going to test three methods to rid the riverbank of carrizo cane, which has thick stalks. Trails through the cane can be all but invisible from higher up on the bank.

One method calls for the cane to be cut by hand and the stumps painted with the herbicide. Another involves using mechanical equipment to dig the cane out by the roots, possibly without the need for the herbicide.

The third and most controversial removal method calls for using helicopters to spray imazapyr directly on the cane, until all plant life in the area is poisoned.

The cane is a non-native plant introduced by Spanish explorers centuries ago. Johnson-Castro said he has no issue with removing the cane, just the method.

The border patrol said that after using the herbicide it intends to replant native vegetation.

Laredo mayor Raul Salinas said he believes federal officials when they say testing shows the chemical is not dangerous, but he also realises opponents have concerns.

"It is a complicated situation because we have to think about protecting our border," said Salinas, a retired FBI agent. "But let's do it in a sensible, reasonable way to make sure humans won't be harmed, nor the vegetation, nor the animals, nor the environment."