US President Donald Trump has attacked “sleazy New York Democrats” after the state’s attorney general sued him and his namesake foundation.

New York’s Attorney General Barbara Underwood is suing Mr Trump and the Donald J Trump Foundation, saying the nonprofit should be dissolved after more than a decade of illegal conduct, including support for Trump’s 2016 US presidential campaign.

Ms Underwood accused the foundation and its directors of conducting “extensive unlawful political coordination” with the campaign, and “repeated and wilful self-dealing” to benefit Trump’s personal and business interests.

“The Trump Foundation was little more than a chequebook for payments from Mr Trump or his businesses to non-profits, regardless of their purpose of legality,” Ms Underwood said in a statement on Thursday local time.

“That is not how private foundations should function.”

The President responded to the lawsuit on Twitter, attacking former New York Attorney General Eric Schneiderman and saying he would not settle the case.

“The sleazy New York Democrats, and their now disgraced (and run out of town) A.G. Eric Schneiderman, are doing everything they can to sue me on a foundation that took in $18,800,000 and gave out to charity more money than it took in, $19,200,000. I won’t settle this case!” Mr Trump wrote.

The sleazy New York Democrats, and their now disgraced (and run out of town) A.G. Eric Schneiderman, are doing everything they can to sue me on a foundation that took in $18,800,000 and gave out to charity more money than it took in, $19,200,000. I won’t settle this case!…

— Donald J. Trump (@realDonaldTrump) June 14, 2018

“Schneiderman, who ran the Clinton campaign in New York, never had the guts to bring this ridiculous case, which lingered in their office for almost 2 years. Now he resigned his office in disgrace, and his disciples brought it when we would not settle.”

Mr Trump’s children were also named as defendants in the attorney general’s petition, filed with the New York State Supreme Court in Manhattan.

New York is also seeking $US2.8 million ($3.7 million) of restitution plus penalties, a 10-year ban on Mr Trump serving as a director of a New York non-profit, and one-year bans for his children Donald Jr, Eric and Ivanka.