Donald Trump has tried to convince lawmakers of the need for a US-Mexico border wall by making an entirely false claim about levels of crime in a Texan city.

Addressing members of Congress in his State of the Union speech on Tuesday evening, the US president wrongly claimed El Paso, which sits on the border with Mexico, had been transformed since the installation of a “powerful barrier”.

“The border city of El Paso, Texas, used to have extremely high rates of violent crime — one of the highest in the entire country, and considered one of our nation's most dangerous cities,” Mr Trump said.

“Now, immediately upon its building, with a powerful barrier in place, El Paso is one of the safest cities in our country.

“Simply put, walls work and walls save lives. So let's work together, compromise, and reach a deal that will truly make America safe.”

In fact, El Paso has never been one of the most dangerous cities in the US and already had one of the lowest crime rates among the country’s large urban areas before construction of a 57-mile border fence began in 2008.