Hooded armed men from the police and Department of State Service (DSS) filtered access to the two chambers -- the Senate and House of Representatives -- preventing lawmakers, workers, journalists and other visitors from entering.
The presidency denied authorising the move, which comes amid a surge of tension between President Muhammadu Buhari and political rivals. Vice President Yemi Osinbajo - who is acting as head of the country while Buhari is on holiday, ordered the dismissal of DSS chief Lawal Musa Daura "with immediate effect".
He described the "unauthorised takeover" of the National Assembly as "a gross violation of constitutional order" and "rule of law".
The DSS has often been accused of high-handedness and abuses against perceived political opponents of the Buhari administration. Parliament began a two-month recess on July 24.
Independent sources speculated that Tuesday's action was a show of strength connected to a political crisis ahead of presidential and parliamentary elections next February.
Saraki, the country's third-highest ranking politician, last week dumped the APC for the main opposition Peoples Democratic Party (PDP).
The APC has called on him to resign, suspecting him to be the force behind defections that have damaged the party's standing and Buhari's chances of re-election.
On the last day before recess, 14 members of the 109-seat senate and 37 members of the 360-seat House of Representatives left the APC. Party primaries are due between this month and October, coinciding with mounting discontent at Buhari's style of government and handling of widespread violence across the country.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)