Melania Trump's parents granted American citizenship via mechanism her husband has repeatedly condemned

'This golden experiment, these doors that are in America, remain hinged open to beautiful people as they have today'

The president has pushed for restrictive immigration policies since moving into the White House (AFP/Getty)

The parents of Melania Trump have been sworn in as US citizens after completing a path to naturalisation her husband has repeatedly attacked and promised to severely curtail.

Viktor and Amalija Knavs took their oaths to become Americans after the first lady sponsored their green cards. President Trump has said most family-based immigration, which he refers to as "chain migration", should end.

“Under the current broken system, a single immigrant can bring in virtually unlimited number of distant relatives,” he said during his State of the Union speech this year.

“Under our plan, we focus on the immediate family by limiting sponsorships to spouses and minor children. This vital reform is necessary, not just for our economy, but for our security and our future.”

The Knavs are originally from Slovenia, where their daughter was born and raised before moving to the US, where she worked as a model before becoming Donald Trump’s third wife.

Speaking after the ceremony in Manhattan, their lawyer, Michael Wildes, said the Knavses had applied for citizenship on their own and did not get any special treatment.

"This golden experiment, these doors that are in America, remain hinged open to beautiful people as they have today," Mr Wildes said.

Since entering the White House, Mr Trump's treatment of people wanting to come to the US has caused outrage across the country and around the world.

Draconian restrictions on people entering from Muslim-majority countries triggered protests across the US and in the countries affected.

His administration's separation of children from families crossing the border illegally — for which he blamed the Democrats — has also provoked widespread condemnation.

The White House recently launched a taskforce aimed at weeding out naturalised citizens who lied during their process to become citizens.

Reports say his administration intends to make it harder for immigrants to get a green card or become a citizen if they have used benefits like Obamacare, children's health insurance, or food stamps.

However, Mr Wildes said the Knavses' success attaining citizenship was "an example of it going right."