Abuja - Nigerian police fired teargas inside the parliament complex on Thursday, apparently trying to block opposition lawmakers, including the speaker of the lower house, from entering the building for a key security vote.
Members of the House of Representatives had been scheduled to vote on a government request to extend emergency rule in the northeast region hit hardest by Boko Haram militants.
The opposition has said it was against the move, and political tensions have been ratcheted up ahead of elections scheduled for February.
Senate President David Mark, a ruling party stalwart, ordered the immediate closure of both chambers over the incident.
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The focus of the police aggression appeared to be lower house speaker Aminu Tambuwal, whose defection to the opposition last month outraged the ruling Peoples Democratic Party (PDP).
The PDP has tried to remove Tambuwal from the speaker's chair and stripped him of his security detail.
Lawmakers scale fence
Tambuwal arrived at parliament at about 10:00 am (0900 GMT) before the vote on the state of emergency extension, his spokesman Imam Imam told AFP.
President Goodluck Jonathan has said the extension is needed to sustain the military offensive against Boko Haram.
But the main opposition All Progressives Congress (APC) has described the strategy as a complete failure, noting the huge Islamist gains since emergency rule was first imposed in May 2013.
Imam said Tambuwal was moving in a convoy with more than 40 other lawmakers, which police repeatedly tried to stop as they approached the main gate of parliament.
The convoy pressed through several police barricades before officers locked the gate that leads into the parliament complex, he added.
Lawmakers began pushing aggressively on the bars to force their way through, with police looking on from the other side, footage on the private Channels television station showed.
Several scaled the gate and then walked with Tambuwal towards the legislative building, the footage showed.
"As soon as we got (to parliament), they insisted he will not enter the chamber," Imam told AFP.
"It was in that midst of confusion that they now used the tear gas on the speaker" and other lawmakers, he added.
An AFP correspondent said the main lobby outside the lower house chamber was filled with tear gas, with bystanders choking as they tried to find their way outside.
Senate president Mark described the chaos as "a very unfortunate incident" and closed both chambers of the National Assembly until Tuesday, meaning Jonathan's emergency rule extension will not be approved this week.
Police spokesman Emmanuel Ojukwu told AFP that police officers were not involved in the incident but that claim was not consistent with witness reports and video footage.
The PDP, which has controlled the government since democracy was restored in 1999, has found itself in uncharted waters in recent months following a wave of lawmaker defections to the APC.
While the PDP currently holds fragile majorities in both chambers, the situation has been in flux throughout the year.
The defection of Tambuwal was seen as blow to Jonathan, who had previously relied on a compliant lower house.
The speaker had been mulling a possible bid for the presidency on the APC ticket at next year's elections but declined earlier this week.
Human rights lawyer Jiti Ogunye said Thursday's fracas recalled the years after Nigeria's independence from Britain in 1960, when a divided civilian government was ultimately overthrown by the military.
"We are in a state of anarchy," he said. "This is how sad our democracy has turned."