Melania Trump denied she broke any immigration laws when she first modelled professionally in the US, in the latest controversy to hit her husband Donald's presidential campaign.
The Republican nominee has made illegal immigration a key part of his campaign platform, and his wife often cites her path to US citizenship in defence of his hard line.
The former Melania Knauss, who is from Slovenia, says she came to the US legally and other aspiring Americans should follow her example.
However several news organisations speculated whether nude photos taken of her in New York in 1995 were evidence that she had worked illegally in the US before securing the appropriate visa.
Mrs Trump used Twitter to dispute that she violated immigration laws.
"I have at all times been in full compliance with the immigration laws of this country. Period. Any allegation to the contrary is simply untrue," she wrote.
She has said she went to the US in 1996 on a visa, got her green card in 2001 and became a US citizen in 2006, the year after she married Mr Trump.
In her statement, Mrs Trump did not specify which visa she held during the early part of her modelling career in New York.
Her former agent told The Associated Press that she obtained a work visa before she modelled professionally in the US in the mid-1990s.
Paolo Zampolli said while he was a partner at modelling agency Metropolitan Models, he secured a work visa for Mrs Trump.
"I know she was not working a paid job before she got the H-1B," Mr Zampolli said, referring to the type of work visa that US companies can obtain for "fashion models of distinguished merit and ability".
H-1B visas generally allow a person to work and live in the US for three years with the opportunity to renew the visas for another three years.
He said he based the H-1B application on Mrs Trump's previous modelling work in Paris and Milan: "We used whatever she did before to get her a visa. She had enough tear sheets to qualify."
In interviews earlier this year with MSNBC and Harper's Bazaar, Mrs Trump's comments appeared to be inconsistent with holding a work visa.
"I never thought to stay here without papers. I had a visa. I travelled every few months back to the country to Slovenia to stamp the visa," she said during the MSNBC interview.
US immigration law did not require such trips that Mrs Trump describes for work-visa holders at the time.
People who hold visitor visas would be required to leave the country on or before the end date of their authorised stay. US law does not allow someone to use a visitor visa to regularly live and work in the country.
Mr Zampolli said he believes Mrs Trump was confused about her visa requirements, noting that she travelled to Slovenia to visit her family numerous times.
He said he was not aware whether she ever held a different visa. It was possible she came to the US on a visitor visa to check out the modelling agency, a practice he said was common when foreign models were considering making the jump to New York.
"They come to meet the client to see if they really should come to New York," he said, noting that the process often includes taking photos to build a portfolio to attract bigger-name modelling contracts.
The photographer who took the nude pictures, Jarl Ale de Basseville, said Mrs Trump was not paid for the photo shoot.
Mr Trump's presidential campaign declined to clarify her comments, discuss Mrs Trump's immigration history in detail or provide copies of any paperwork that would put the issue to rest.