Police investigate '8647' written in grass on US national mall

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 discoloration 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 sea shells.

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 $13.1 to repaint the Lincoln Memorial reflecting pool, as well as a plan to build an arch decorated with golden figures including lions and eagles.