public safety".

Mark Rosenbaum, one of Mr Ramirez's lawyers, said he "unequivocally denies being in a gang".

Media playback is unsupported on your device Media caption Ramon Mendoza, an undocumented immigrant, is facing - and fighting - deportation

He said Mr Ramirez had been "repeatedly pressured" by customs agents to falsely admit to gang links while in custody.

Mr Ramirez's legal team say this could be the first time under the Trump administration that a person covered by the Deferred Action for Childhood Arrivals, or DACA, has been taken into immigration custody.

DACA was established in 2012 by President Obama to allow those brought to America while young to attend school and work without fear of deportation.

There are more than 740,000 people in the programme.

They are often known as "dreamers" - a nametaken from the failed 2010 DREAM Act (Development, Relief and Education for Alien Minors) - a bill which aimed to help young illegal immigrants become US citizens.

Image copyright Getty Images Image caption President Trump has not clarified his official policy on DACA

The arrest is being seen as significant given Mr Trump's long-standing promise of an immigration clampdown.

In January, he issued an executive order expanding the remit of Homeland Security officials so they can target not only immigrants with serious criminal records, but also those with minor offences or no convictions to their names.

Hundreds of undocumented migrants have been arrested in recent days, in at least 11 states.

'Keeping my campaign promise'

"The crackdown on illegal criminals is merely the keeping of my campaign promise," the president wrote on Twitter. "Gang