Zambia's long-time opposition leader Michael Sata has been sworn in as president, marking the country's second democratic transition of power since its independence from Britain.

The electoral commission announced early Friday that the 74-year-old populist leader defeated incumbent candidate Rupiah Banda after a tight presidential race.

In a tearful news conference, President Banda conceded defeat, saying that “the people of Zambia have spoken and we must all listen.” He urged supporters to reject acts of retribution, saying “now is not the time for violence.”

Supporters of Mr. Sata took to the streets in celebration after the announcement by the electoral commission, which came just after midnight local time.

After Tuesday's poll, there were scattered reports of violence across the country amid frustration over the slow release of election results. Many opposition members said they feared the delay would allow time for the commission to skew the results in Mr. Banda's favor.

Ahead of the poll, Mr. Sata, known as “King Cobra” for his sharp wit and fiery speeches, accused the electoral commission of planning to rig the outcome using pre-marked ballots – an allegation the commission denied.

European Union election observers said Thursday that the elections were “generally well administered,” but unequal access to resources meant there was not a “level playing field” for campaigning.

Specifically, observers criticized state-owned media for failing to meet “even their minimal obligations as public service media,” saying state news programming lacked balance in its coverage of the campaign.

Analysts do not expect many major policy changes when Mr. Sata takes office, though his Patriotic Front party has promised to re-instate a 25 percent windfall tax on mining revenues that Banda's party abolished in 2009.

Mr. Sata's repeatedly accused Mr. Banda of tolerating corruption and not doing enough to ensure that more Zambians share in the wealth of the country's copper reserves. Zambia is Africa's biggest producer of copper.

The two men are long-time rivals. In 2008, Mr. Banda defeated Mr. Sata by two percentage points in a special election triggered by the death of late President Levy Mwanawasa, who died of a stroke.

Mr. Banda's Movement for Multiparty Democracy had ruled the country since former president Frederick Chiluba defeated independence leader Kenneth Kaunda in the country's first democratic elections held in 1991.

Formerly known as Northern Rhodesia, Zambia declared independence from Britain in 1964.