An Occupy Congress movement shut down the White House for one hour late Tuesday night with a smoke bomb thrown over the Pennsylvania Avenue fence.
No one was injured, but White House personnel and reporters were prohibited from leaving the building for nearly an hour and then through a side entrance while security personnel investigated the incident. Robots were deployed to check for other devices.
President Barack Obama and his wife Michelle were outside the White House facility at the time and returned under tight guard as the investigation was under way.
No arrests were made, but further away from the White House, police took four people into custody after a scuffle near the Capitol.
An estimated 1,000 protesters had gathered on the main artery to demonstrate against corporate influence in the government. Rally organizers had secured a permit that allowed up to 10,000 people to attend the rally.