US police are investigating a large imprint of the numbers 8-6-4-7 that were apparently drawn in the grass of the National Mall in Washington, DC.

"Eighty-six" is a slang term for "get rid of", and Trump administration officials claim that the numbers are meant to encourage violence against Trump, the 47th president.

US Park Police "responded to a report of vandalism" at around 11:30ET (16:30GMT) on Thursday morning, the agency said in a statement.

"The cause of the discolouration has not yet been determined. Grass samples have been collected for testing. The investigation is ongoing."

Images of the grass show the numbers 8, 6 and 7, but the number 4 is not clearly visible.

The investigation comes as US prosecutors attempt to jail the former director of the FBI for a social media post in which the numbers were seen written on a beach in seashells.

James Comey is facing multiple charges related to an alleged threat to kill Trump. He has denied the charges and called the prosecution politically motivated.

The numbers have been used by opponents of Trump, and have appeared at protests against his administration.

The slogan written in the grass appears somewhat faded, with the number 8 appearing more prominently than the others. It is located close to the World War 2 memorial.

The alleged vandalism comes amid a beautification campaign of US monuments in the city, led by Trump. The campaign includes $13.1m (£9.6m) to repaint the Lincoln Memorial reflecting pool, as well as a plan to build an arch decorated with golden figures, including lions and eagles.