A new row has erupted around the president as he and his staff have been involved in a back-and-forth involving his daughter's fashion line, with one adviser being accused of violating ethics laws.

Nordstrom, a luxury department store chain, announced last week that they would be dropping Ivanka Trump's fashion line after poor sales.

The president weighed in on Twitter, saying that his daughter had been "treated unfairly".

White House press secretary Sean Spicer was forced to back up Trump's statement, saying that the company's decision to drop her fashion line was a "direct attack" on the president and his policies.

Kellyanne Conway, who advises the president, appeared on the Fox News show "Fox and Friends", and directly told viewers to "go buy Ivanka's stuff".

Her remarks seem to violate a regulation by the Office of Government Ethics, which bans staff from endorsing products or companies and also bans them from using public office for private gain of themselves or someone else.

The Office of Government Ethics website appears to be down as a result of the row.

Sean Spicer later said in a White House press briefing that Conway had been "counselled" on her comments.

Nordstrum say they made the decision and informed Ivanka in January, before the president was sworn in.

The company said in a statement: "Sales of the brand have steadily declined to the point where it didn't make good business sense for us to continue with the line for now.

"We've had a great relationship with the Ivanka Trump team... Ivanka was personally informed of our decision in early January."

Conway's comments have been slammed by ethics watchdog Citizens for Responsibility and Ethics in Washington.

Executive director Noah Bookbinder said in a statement: "The law is clear that public officials should not use their offices for their own private gain or the private gain of others.

"It's hard to find a clearer case of that kind of misuse of office than we saw today."