Building a wall along the U.S.-Mexico border has been a key promise of President Donald Trump's 2016 electoral campaign. But on Wednesday, the U.S. president puzzled his audience by claiming he plans to build a wall in Colorado, which lies well within the country's territory and doesn't have an international border.

The western U.S. state is about 600 kilometers north of Mexico and 1,000 kilometers south of Canada. However Colorado, to its south, does have the southwestern state of New Mexico, which shares a border with Mexico.

"You know why we are going to win New Mexico? Because they want safety on their border," Trump said addressing an energy conference in Pittsburgh. "And we are building a wall on the border of New Mexico, and we are building a wall in Colorado," he revealed.

"We are building a beautiful wall, a big one that really works, that you can't get over, you can't get under," Trump elaborated.

"And we are building a wall in Texas, and we are not building a wall in Kansas, but they get the benefit of the walls that we just mentioned," he added.

Trump's unusual claim became a source of bemusement on social media, where he was widely ridiculed.

Colorado Governor Jared Polis derided the president on Twitter pointing out the obvious flaw in his comment. "Well this is awkward... Colorado doesn't border Mexico."

"Good thing Colorado now offers free full day kindergarten so our kids can learn basic geography," Polis added mocking Trump's apparent lack of knowledge about geography and maps.

Polis's predecessor former Colorado governor John Hickenlooper took a snipe at Trump as well.

Democratic Senator from Vermont, Patrick Leahy, in a mocking post on Twitter, shared a map showing a new international border drawn around New Mexico in black ink and a line erasing the first half of the state's name so that it reads: Mexico.

On Facebook, Bob Duff, Democratic Majority Leader of the Connecticut Senate, queried: "Did the president give away New Mexico to Mexico or New Mexico to Colorado? Apparently, Colorado is now a border state."

The U.S. shares a border with Mexico along the states of Arizona, California, New Mexico and Texas. Construction of a wall along the U.S.-Mexico border to prevent migration was the hallmark of Trump's electoral campaign.

The Trump administration has been criticized for diverting funds from military projects to build the promised wall purportedly to stop migrants on the U.S.-Mexico border entering the country. Reports reveal much of the wall has been erected in areas where barriers already existed without any substantial construction along new or undefended stretches of the border.

The Republican-controlled Senate failed last week to overturn the national emergency declaration the president had used to pay for the wall's construction. Earlier in September, the Pentagon moved to divert 3.6 billion U.S. dollars of military construction funding from 127 projects around the world to pay for 11 wall projects in a move that angered several lawmakers.

The U.S. president invoked national emergency in February after he failed to convince the Congress to allocate additional funding for the wall. After the Congress rejected the funding proposal, Trump retaliated with his first veto.

As per the law, the Congress can challenge the emergency declaration every six months but it has failed to override the presidential decree so far.