NEW YORK (REUTERS) - The New York state attorney general has filed a US$40 million (S$51.2 million) lawsuit against Donald Trump's for-profit investment school, Trump University, accusing it of engaging in illegal business practices, according to the New York Times.

The newspaper reported that New York Attorney General Eric Schneiderman alleged that the real estate mogul, his Trump Organization company and others made false claims about classes at the school, including that Mr Trump handpicked instructors.

Representatives for the New York attorney general's office and Mr Trump were not available for comment late on Saturday.

But Mr Trump said in a post on Twitter, "Light weight NYS Attorney General Eric Schneiderman is trying to extort me with a civil law suit." The tweet linked to a website about Trump University, which says the school has a 98 percent approval rating from students.

The New York attorney general's lawsuit seeks restitution of at least US$40 million, the Times said, and it alleges that Trump University was run as an unlicensed educational institution from 2005 to 2011 and that Mr Trump did not create the curriculum for any of the school's courses.