“Now, there are certain places you don’t need a wall, because you have, you know, you have mountains, you have other things. You have large and rather vicious rivers," the President-elect said in an interview with Fox News in Cincinnati, Ohio during his so-called "Thank You" tour.
Mr Trump failed to specify where these natural obstacles are located, but insisted this was not a u-turn on the pledge, which became a key part of his White House campaign.
"We’re building a wall, it’s going to be a real wall because we’re going to stop the drugs from coming in, we’re going to have people come in but they’re going to come in legally and we’re going to have a great wall, a real wall and we’re going to stop what’s happening, because what’s happening in our country is very sad in so many different ways," Mr Trump said.
The Republican's comments come after he was accused of back tracking on his pledge to build the border wall when he said some parts of the barrier would actually be a fence.
"There could be some fencing," he told CBS News last month in his first interview following his surprise election victory. "For certain areas I would [accept a fence], but certain areas, a wall is more appropriate. I’m very good at this, it’s called construction."
The border between the US and Mexico stretches over 3,200km between California and Texas and is the world's most frequently-crossed controlled international boundary.
There is currently a series of relatively short walls and fences designed to prevent illegal border crossings and a system of sensors and cameras monitored by Border Patrol forces where there is no physical barrier in place.
In November, Mr Trump explained that once the border is “secure”, then the Bureau of Immigration and Customs Enforcement will assess the status of the remaining undocumented immigrants in the country, promising to deport or incarcerate two to three million people living in the country illegally who “are criminal and have criminal records, gang members, drug dealers.”
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