Egyptian troops with armoured vehicles have secured the central Cairo studios of state television on Wednesday, security sources said.
As a deadline approaches when the army high command is expected to step in and reorder Egypt's political institutions, the sources said staff not involved in working on live broadcasts had left the building.
Egypt's army also said it had set no times for issuing statements or speeches on Wednesday as a deadline loomed that would trigger a military takeover backed by protesters.
Army sources had previously said the army would issue a statement after the deadline expires at about 5 pm (1500 GMT).
The military had on Monday given politicians 48 hours to agree a resolution of the political standoff, saying that if they failed to do so, it would impose its own road map.