A 32-foot smuggling tunnel has been unearthed on the Arizona-Mexico border, reportedly the third tunnel found in the area in less than a month.

According to a tweet on Wednesday from the Mexican Federal Police, the latest tunnel was uncovered across the border from Nogales, Arizona. Officials claimed the tunnel was used "for the transfer of drugs and people".

A video posted to social media shows officers opening a manhole in the drainage system and shining a light in. One of the officers then slides through the hole to search the passage.

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The footage follows the discovery of two other tunnels, a 50-foot one and a 65-foot one, in the same area.

The third find comes in the midst of the longest government shutdown in US history: the American government has now been closed for 24 days, due to President Donald Trump's demand for a $5.7 billion border wall.

Many opponents of building more border walls – there are already roughly 700 miles of wall on parts of the southern border - point to tunnels as an example of why border walls do not work.

It has been reported that some 800,000 federal employees have been forced to go on unpaid leave or work without pay since December 22 because of the government shutdown.

As the closure enters its fourth week, it shows no signs of resolution, leaving many wondering how they will make ends meet.

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Trump's administration is now being sued by a group of federal employees, who accuse both the president and their bosses of violating the 13th Amendment, which abolished slavery and involuntary servitude in the aftermath of the Civil War.

Employees at U.S. Customs and Border Protection, the Bureau of Prisons and Federal Aviation Administration have already filed lawsuits against the administration through their respective unions, among others.

But the former reality TV star has insisted that the Democrats are to blame, claiming that they were using the break for "vacation" time.

"I do have a plan on the Shutdown," he wrote on Twitter. "But to understand that plan you would have to understand the fact that I won the election, and I promised safety and security for the American people."

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He continued: "Part of that promise was a Wall at the Southern Border. Elections have consequences! We will be out for a long time unless the Democrats come back from their ‘vacations’ and get back to work. I am in the White House ready to sign!"

However, rather than holding the Democrat Party responsible, a Washington Post-ABC News poll published Sunday showed that Americans blame the situation on Trump.

When asked, "Who do you think is mainly responsible for this situation?" 53 per cent of Americans claimed they blamed the president and congressional Republicans.

In addition, 29 per cent blamed Democrats and 13 per cent said both sides were equally responsible, while four per cent had no opinion on the matter.

A 32-foot smuggling tunnel has been unearthed on the Arizona border