Zambia's High Court has barred three private media organizations from publishing speculative reports on the outcome of Tuesday's presidential and parliamentary elections, as the country's electoral commission scrambles to finish counting votes ahead its self-imposed Thursday deadline.

The court issued an injunction Wednesday banning one of the country's leading privately-owned, pro-opposition newspapers, The Post of Zambia, and two other media outlets from publishing stories announcing preliminary results before the numbers are officially announced. The injunction came after The Post ran a headline claiming “Sata heads for victory” on the day after the election.

On Thursday, unidentified hackers attacked the website of Zambia's Electoral Commission, posting a string of statements claiming that opposition leader Michael Sata of the Patriotic Front party was in the lead over incumbent Rupiah Banda of the Movement for Multiparty Democracy.

The latest partial results from the election body suggest Mr. Sata does hold a slight lead over Mr. Banda. Analysts say Mr. Sata's early lead has been boosted by a strong performance in Zambia's urban areas, where votes are likely to be counted more quickly. Mr. Banda is expected to perform stronger in the countryside.

Meanwhile, there were scattered reports of rioting by opposition protesters on Thursday, amid frustration that the electoral commission is counting the votes too slowly. Rioters took to the streets while throwing stones in Zambia's second biggest city Kitwe, as well as several other areas. Scattered incidents of violence were also reported Tuesday in the capital, Lusaka.

Opposition parties already have complained that the delay in releasing the results may be a ploy to allow the commission to skew results in favor of President Banda.

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.

The electoral commission has said it aims to have complete results from all 150 constituencies by the end of the day on Thursday.

Ahead of the poll, Mr. Sata accused the electoral commission of planning to rig the outcome using pre-marked ballots. The electoral commission has denied that allegation.

President Banda campaigned on a record of several years of strong economic growth in copper-rich Zambia, which has benefited from a boom in global commodity prices. Mr. Sata's Patriotic Front 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.

Mr. Banda defeated Mr. Sata by two percentage points in a 2008 special election to complete the term of the late President Levy Mwanawasa, who died of a stroke.

Mr. Banda served as Mr. Mwanawasa's deputy. Mr. Sata disputed those election results, and his supporters rioted for days afterward.

More than 5 million Zambians were registered to vote in Tuesday's presidential, parliamentary and local elections.