The MDC MPs were overjoyed at Lovemore Moyo's victory
The candidate of Zimbabwe's opposition MDC has been elected speaker of parliament, after MPs were sworn in following elections five months ago.
MDC chairman Lovemore Moyo becomes the first opposition speaker since the country's independence in 1980.
As the MPs arrived for the ceremony, two MDC law-makers were arrested, a party spokesman said.
President Robert Mugabe's Zanu-PF did not field a candidate for the vote, but backed a rival MDC faction.
The BBC's Karen Allen says this was a tactic to try and engineer control of parliament, which has backfired.
However, the Zanu-PF candidate was elected to be president of the upper house, the Senate, reports Reuters news agency.
As a result of the March elections, the breakaway MDC (Movement for Democratic Change) faction holds the balance of power in the House of Assembly.
They have chosen the path of arrogance, unilateralism that's a serious blow to confidence-building in the talks
Nelson Chamisa, MDC
But Mr Moyo won with 110 votes, against 98 for Paul Themba Nyathi from the smaller faction.
Our correspondent says the results mean at least one Zanu-PF MP voted for Mr Moyo in the secret ballot.
The MDC has 100 seats - one seat more than President Robert Mugabe's Zanu-PF - while the Arthur Mutambara-led MDC faction has 10 seats.
MDC leader Morgan Tsvangirai opposed the recall of parliament, which Mr Mugabe is to officially open on Tuesday.
He says it could jeopardise power-sharing talks, which are currently deadlocked.
After being sworn in, the opposition MPs sat on the government benches, reports the AFP news agency.
"You sit on that side. You are now in the opposition," they shouted at their Zanu-PF rivals.
Celebrations for Lovemore Moyo's election as speaker
MDC MPs sang and cheered when it was announced that Mr Moyo had won the vote and carried him shoulder-high.
Zanu-PF's Rural Housing Minister Emmerson Mnangagwa, long seen as a possible successor to Mr Mugabe, offered his congratulations.
"Mr Speaker, Sir. This is a truly historic event and I would like, on behalf of the president, our party and this side of this august House, to congratulate you," he said in parliament, Reuters reports.
The MDC had warned that 15 of its MPs would not attend the swearing-in ceremony, as they were in hiding following a state-sponsored campaign of violence.
The police had accused them of murder, rape and political violence.
House of Assembly * MDC Tsvangirai: 100 * Zanu-PF: 99 * MDC Mutambara: 10 * Independent: 1
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