The brief "unauthorized takeover" of parliament has come amid tensions between President Muhammadu Buhari's ruling APC and the main opposition. The opposition labeled the incident an attempted "legislative coup."
Police and security forces temporarily blockaded the entrance to Nigeria's National Assembly on Tuesday, in what the presidency described as rogue action to take over the parliament.
Hooded police and members of the Department of State Service (DSS) prevented lawmakers, journalists and legislative aides from entering the National Assembly for several hours.
The incident happened as tensions flare between President Muhammadu Buhari and the opposition in a brewing political standoff ahead of parliamentary and presidential elections early next year.
An aide to the Senate president posted videos on Twitter of the standoff in front of the parliament, describing the scene as a "legislative coup."
The aide, Bamikole Banks Omisore, said security forces tried to prevent lawmakers not loyal to Buhari and Vice President Yemi Osinbajo from entering the parliament.
Some lawmakers later forced their way into the National Assembly building, which is home to the House and Senate. Both bodies are currently in recess.
Osinbajo is acting president while Buhari is out of the country on vacation.
On Tiuesday, Osinbajo's office announced that the head of DSS, Lawal Musa Daura, had been sacked.
In a statement, he said there was a "completely unacceptable" and "unauthorized takeover of the National Assembly."
The apparent rogue action by security forces comes as members of Buhari's All Progressives Congress (APC) are seeking the removal of the Senate president, Bukola Saraki.
Saraki, the country's No. 3 politician, abandoned the APC and joined the main opposition Peoples Democratic Party (PDP) on the last day before recess on July 24.
Fourteen members of the 109-seat Senate and 37 members of the 360-seat House also abandoned the APC. Several state governors have also defected from the APC to PDP in recent weeks.
The APC blames Saraki for orchestrating the mass defections, which come in the run-up to presidential and parliamentary elections in February 2019.
Atiku Abubakar, a former vice president and PDP presidential hopeful, described the security forces' operation in front the parliament as an "illegal and undemocratic attempt by fascist forces ... to force a change in the Nigerian Senate's leadership."
The defections represent a major blow for Buhari's chances of being re-elected, as he has lost influential figures and patronage networks.
The former military ruler is under pressure for his handling of rising violence surrounding land disputes between farmers and herders, which has claimed at least 1,300 lives since January. He also faces criticism over the military's ongoing campaign against Boko Haram militants.
There are also questions about the 75-year-old's health.
cw/rc (AFP, Reuters)