The Secret Service arrested a man in Lafayette Park on Wednesday afternoon following suspicious activity near the White House, witnesses report. Reporters at the White House say the man threw something over the fence near the North Lawn, prompting a "suspicious package" response from law enforcement.

CNBC's Eamon Javers said he saw a black robot on the White House lawn:  

According to the Associated Press's White House reporter and other journalists on Twitter, who ever threw the object was quickly arrested.

Witness Jon Rich took a photo of police cars by Lafayette Park as officials asked individuals to clear out and posted it to Twitter:

Pennsylvania Avenue in front of the White House was briefly cleared, but has since re-opened. Officials have not provided any information on what the object was, but we will update this story as details become available.