New York: President Donald Trump's longtime confidant Roger Stone has apologised to the judge presiding over his criminal case for an Instagram post featuring a photo of her with what appears to be the crosshairs of a gun.

Stone and his lawyers filed a notice in court on Monday night saying Stone recognised "the photograph and comment today was improper and should not have been posted".

In reply, US District Judge Amy Berman Jackson ordered Stone to appear in court on February 21 for a hearing to decide whether his bail conditions will be revoked in light of the post.

Stone posted a photo on Monday of Jackson with what appeared to be crosshairs near her head.