Nigerian security forces have fired tear gas inside parliament, just before a crucial debate on security in the conflict-ridden north-east.
Reports say the police were trying to stop House of Representatives speaker Aminu Tambuwal from entering.
Mr Tambuwal defected to the opposition from the ruling PDP last month. His former colleagues have since argued he should be stripped of his speaker role.
Senate leader David Mark ordered both chambers to close until next week.
Political tensions are high in Nigeria, ahead of general elections next year.
It is a coincidence that this row happened on a day when an important bill was to be debated by the lawmakers.
After the defection of the speaker of the House of Representatives from the ruling People’s Democratic Party (PDP) to the opposition, PDP members have publicly called for his impeachment.
Lawmakers from the ruling party even tried to recall the House from its recess, but the courts decided that only the speaker is constitutionally empowered to do so.
Last month the Nigerian police withdrew the security aides attached to Aminu Tambuwal after his defection, saying he ceased to be the speaker of the house.
Nigerian police are notorious for being partisan and actively support the wishes of whoever is in power.
If Mr Tambuwal had been absent from Thursday’s crucial sitting, PDP lawmakers could have impeached him and proceeded to approve the extension of the state of emergency with little opposition.
Mr Tambuwal’s defection is a further blow to President Goodluck Jonathan, who is seeking re-election in February.
Mr Tambuwal adjourned the House shortly after he defected in late October, apparently to ensure he could not be unseated by PDP representatives.
Thursday was the first full session of the House since his defection.
Parliamentarians were due to debate a presidential bill seeking the extension of the state of emergency in three states hardest hit by the militant group Boko Haram.
BBC Hausa editor Mansur Liman says many opposition MPs opposed the extension of the state of emergency because they say it has failed to bring an end to the insurgency.
Witnesses said security agents attempted to block Mr Tambuwal as he arrived at parliament, and also locked out other opposition politicians.
Images showed suited politicians scaling the gates outside of the assembly building.
Agents then fired tear gas, which filled the lobby for several minutes.
Mr Tambuwal reportedly managed to get into the assembly building only after other politicians scuffled with security agents.
Credit: BBC
