Trump's in-laws become US citizens using 'chain migration', which he criticises

President Donald Trump's Slovenian in-laws became United States citizens through "chain migration", a programme he has repeatedly denounced, in which adult American citizens can obtain citizenship for their relatives.

First Lady Melania Trump's parents, Viktor and Amalija Knavs, became US citizens at a private ceremony here. She had sponsored her parents for their green cards, their lawyer Michael Wildes said in a report in The New York Times.

"Once they had the green card, they then applied for citizenship when they were eligible," he said.

When asked if the Knavses had obtained citizenship through "chain migration", Wildes, said, "I suppose."

"It's a dirty, a dirtier word," he said, but added that "it stands for a bedrock of our immigration process when it comes to family reunification."

Trump has vehemently opposed the "chain migration" system, more commonly known as family-based immigration, that lets adult American citizens obtain citizenship for their relatives.

In November, he had tweeted, "CHAIN MIGRATION must end now! Some people come in, and they bring their whole family with them, who can be truly evil. NOT ACCEPTABLE!”

Trump also often speaks out against the family-based immigration system at his rallies, saying it a pathway for terrorists to enter the country, the NYT report added.

According to the report, the first lady's communications director Stephanie Grisham said since the Knavses are not part of the administration, she is not commenting on them.

Standing alongside the Knavses, their lawyer said the couple has "travailed a wonderful journey, like most have, millions have in getting citizenship and waiting the requisite period of time."

He said their application, the process, the interview was no different than anybody's else's.

"…These doors that are in America remain hinged open to beautiful people as they have today. They would appreciate their privacy and we just thank everybody for their attention to this very important dialogue that we are having on immigration. This is an example of it going right," he said.

Viktor, 74, is two years older than President Trump. Amalija is 73.

The first lady, born Melanija, changed her name to Melania Knauss when she started modelling.

According to news reports, Melania came to the US in 2001 on a so-called Einstein visa for "individuals of extraordinary ability" as a model.

She became a United States citizen in 2006.

The Knavses came and went from the ceremony at a Manhattan federal building flanked by Homeland Security police.

Melania Trump was not present for the ceremony.

She was in Bedminster, New Jersey, at the Trump National Golf Club, where Trump is currently staying.

The Knavses frequently travel with the Trumps and split their time between New York, Palm Beach and Washington, where they stay in the White House, the NYT report added.

It said it is unclear about when or how the couple received green cards.

Under immigration statutes, the Knavses would have needed to have their green cards for at least five years in order to apply for citizenship, along with fulfilling character, residency and civic knowledge requirements.

According to the US Citizenship and Immigration Services, it takes about 1-2 years to process an application for naturalization in New York City.

The report quoted their lawyer as saying that the couple had met the five-year requirement, but added, "I can't give further comment."

Usually naturalization ceremonies at the Jacob J. Javits Federal Building in the city are large events in which several immigrants are sworn in as citizens after reciting an oath and the Pledge of Allegiance. But the Knavses' lawyer said their ceremony was kept private for "security reasons".

Presiding over the ceremony was New York district director of the US Citizenship and Immigration Services Thomas Cioppa.

The Knavses raised Melania in the rural industrial town of Sevnica while Slovenia was under Communist rule.

Viktor was a car dealer while Amalija worked in a textile factory.