Reports of hate crimes have spiked in New York City and the city's mayor says he believes heated rhetoric by President-elect Donald Trump is a factor.

At a news conference Monday, Mayor Bill de Blasio spoke about allegations that an off-duty Muslim police officer was threatened by a man who told her to "go back to her country."

Asked if he thought Trump was to blame for an increase in similar incidents, the mayor said "It's obviously more complicated than that. It is not linear."

But he accused Trump of using "hate speech" and saying "horrible things" about Muslims.

Police in New York have logged 43 possible hate crimes since Trump's election, double the number during the same period last year.

Trump has denied that his proposals on immigration and restrictions on Muslims entering the U.S. amounted to hate speech.