Donald Trump adviser Stephen Miller was approached by a customer in a Mexican restaurant who called him a “fascist”, amid anger at the US president’s immigration policies, US media reports.

Mr Trump has received widespread criticism after American border guards split at least 2,000 children from their parents at the Mexican border.

Mr Miller played a key role in advancing the tougher border policy and called it a “simple idea” that sends the message “no one is exempt from immigration law”, according to The New York Times.

The White House aide was dining at Mexican restaurant Espita Mezcaleria in Shaw, Washington DC, on Sunday when he was accosted.

“Hey look guys, whoever thought we’d be in a restaurant with a real-life fascist begging [for] money for new cages?” a customer at the restaurant said, according to an unnamed source speaking to the New York Post.

Mr Miller continued his meal at the restaurant after the comment, according to the report.

US homeland security secretary, Kirstjen Nielsen, left another Mexican restaurant in the city on Tuesday when demonstrators entered and shouted: “Shame!”

“In a Mexican restaurant of all places,” one protester could be heard saying in a video of the incident.

Another demonstrator played the restaurant an audio recording of children crying at a detention centre in Texas.

“How does it make you feel?” a protester asked Ms Nielsen.

The US president backed down on Wednesday and signed an executive order stopping children being taken away from their parents. He said he “didn’t like the sight or the feeling of families being separated”.

Family separations have escalated under Mr Trump’s zero tolerance policy, which requires all adults caught crossing the border illegally to be referred for prosecution.

Adults facing charges are housed separately from their children, resulting in the separation of parents from children said to be as young as nine-months-old.

The president’s new executive order states that policy is to “maintain family unity”, except in cases where doing so would threaten a child’s wellbeing.

Undocumented immigration across the US-Mexico border Show all 14 1 /14 Undocumented immigration across the US-Mexico border Undocumented immigration across the US-Mexico border Immigrant children, many of whom are separated form their parents, are housed in Texas' tent city Reuters Undocumented immigration across the US-Mexico border A two-year-old Honduran asylum seeker cries as her mother is searched and detained near the US-Mexico border Getty Undocumented immigration across the US-Mexico border Undocumented migrants ride on the top of a freight train referred to as the beast, or La Bestia Getty Undocumented immigration across the US-Mexico border A cage inside a US Customs and Border Protection detention facility in Texas Reuters Undocumented immigration across the US-Mexico border US Border Patrol Academy All new agents must complete a months-long training course at the New Mexico facility before assuming their posts at Border Patrol stations, mostly along the US-Mexico border Getty Undocumented immigration across the US-Mexico border US-Mexico border fence A group of young men walk along the Mexican side of the US-Mexico border fence in a remote area of the Sonoran Desert Getty Undocumented immigration across the US-Mexico border US-Mexico border fence in the US Man looks through US-Mexico border fence into the US in Tijuana, Mexico Getty Undocumented immigration across the US-Mexico border US-Mexico border fence US Border Patrol agent Sal De Leon stands near a section of the US-Mexico border fence while stopping on patrol on in La Joya, Texas Getty Undocumented immigration across the US-Mexico border US Border Patrol Academy US Border Patrol instructor yells at trainees after their initial arrival to the academy Getty Undocumented immigration across the US-Mexico border Memorial service in Guatemala Families attend a memorial service for two boys who were kidnapped and killed in San Juan Sacatepequez, Guatemala. Crime drives emigration from Guatemala to the United States, as families seek refuge from the danger Getty Undocumented immigration across the US-Mexico border Arrests on the border Undocumented immigrants comfort each other after being caught by Border Patrol agents near the US-Mexico border Getty Undocumented immigration across the US-Mexico border Detention holding facility A boy from Honduras watches a movie at a detention facility run by the US Border Patrol Getty Undocumented immigration across the US-Mexico border Mexican farm workers Mexican migrant workers harvest organic parsley at Grant Family Farms in Wellington, Colorado Getty Undocumented immigration across the US-Mexico border Mexican family in Arizona A Mexican immigrant family sits in the living room of their rented home in Tuscon, Arizona. The family that Arizona's new tough immigrant law had created a climate of fear in the immigrant community. Getty

In the order, Mr Trump directed the secretary of homeland security to house immigrants facing prosecution alongside their family members “to the extent permitted by law and subject to the availability of appropriations”.

He told the secretary of defence to identify any existing facilities for housing immigrant families, and to build more if necessary.