MEXICO CITY, Nov. 6 (Xinhua) -- U.S. President Donald Trump's proposed border wall between the United States and Mexico would be an environmental "disaster," a United Nations official said on Monday.

"The wall is going to be a disaster for different reasons ... and one of the ways is that it is going to be a disaster at the environmental level," John Knox, the UN's special rapporteur on human rights and the environment, said here at a forum on biodiversity.

"Biodiversity and the ecosystems don't care about political borders, they don't stop where the wall begins," Knox said after being asked of his opinion on the controversial measure.

A solid physical barrier could interfere with the movement and survival of regional species, he said. "I hope the wall will not be built."

In late October, it was reported that eight prototypes of the wall have been erected along the border between the U.S. city of San Diego and Tijuana, Mexico.

The nine-meter-high walls made of concrete and other materials are purportedly to be tested to gauge their effectiveness, mainly in keeping out would-be undocumented migrants.

Building a border wall was one of the main promises Trump made during the U.S. presidential campaign last year.