New York: President Donald Trump's long-time accounting firm must hand over eight years of his tax returns to New York prosecutors, a US appeals court has ruled in the latest setback for Trump in his tenacious efforts to keep his finances secret.

The ruling by a unanimous three-judge panel of the New York-based 2nd US Circuit Court of Appeals on Monday, local time, backed the ability of prosecutors to enforce a subpoena for the returns against accounting firm Mazars LLP.

Jay Sekulow, a lawyer for Trump, said the Republican President will appeal the ruling to the US Supreme Court, whose 5-4 conservative majority includes two justices appointed by Trump.

The office of Manhattan District Attorney Cyrus Vance, a Democrat, is seeking the returns as part of a criminal probe into Trump and his family real estate business. The scope of that probe is not publicly known.