The $US250 million ($A355 million) lawsuit by Attorney-General Letitia James last September accused the defendants of involvement in a decade-long scheme to manipulate asset values and Trump's net worth, in order to induce banks and insurers to provide better terms.

On January 26, the defendants filed formal "answers" where, as often occurs in similar lawsuits, they denied or claimed to lack sufficient knowledge about dozens of substantive accusations.

In a letter to the Manhattan judge overseeing the case, Arthur Engoron, James said many responses were "demonstrably false," frivolous or otherwise improper. She said the Trumps should lose some of their defences, as well as face sanctions.

"The court has already admonished defendants and their counsel for their continued invocation of meritless legal claims but exercised its discretion in not imposing such sanctions," the letter said.

"It does not appear that this point was taken."

Lawyers for the Trump defendants did not immediately respond to requests for comment.

James said the improper responses included Trump's objection to being labelled the "inactive president" of the Trump Organisation during his White House term, though he had used that description in an October 2021 sworn deposition.

Trump's daughter Ivanka was criticised by James for saying she did not know whether she had personally met with bankers, or could confirm the contents of her own emails.

James also rejected arguments by Donald Trump and his sons Donald Jr and Eric that she lacked standing to sue and "acted contrary to the ancient and customary norms" governing prosecutors, saying Engoron had already rejected their contention that she was pursuing a political "witch hunt".

Earlier in January, Donald Trump ended two legal challenges to James' lawsuit, after a Florida judge imposed $US937,989 ($A1.3 million) of sanctions against him and his lawyer for filing a "completely frivolous" lawsuit accusing Hillary Clinton of trying to rig the 2016 US presidential election.

James asked for sanctions on the same day new video from her office's August 10 deposition of Donald Trump showed the former president repeatedly refusing to answer questions, citing his right against self-incrimination under the US Constitution.

"This is a vindictive and self-serving fishing expedition, the likes of which this country has perhaps never seen before," Trump said.

"Anyone in my position not taking the Fifth Amendment would be a fool, an absolute fool."

Australian Associated Press