Zambian President Levy Mwanawasa has been re-elected to a second term in office, the country's election authorities have declared.
There has been a second day of rioting in Lusaka
Opposition leader Michael Sata, who came second, said the election had been stolen but urged his supporters to remain calm.
There has been a second day of clashes between armed police and supporters of Mr Sata's Patriotic Front.
Mr Mwanawasa won 43% of the vote in last week's poll while Mr Sata got 29%.
The other main candidate, Haikande Hichilima, won 25% to come third.
Mr Sata acknowledged his rival's victory but said he would make life difficult for Mr Mwanawasa "inside parliament and outside parliament".
He has alleged voter fraud, saying as many as 400,000 votes appeared not to have been counted in areas where he had expected to do well.
He told the BBC there was lots of time to investigate the ballot: "Levy Mwanawasa's term of office does not come to an end until January, 2007.
"We have... three months in which we can clear all of these things and we have [a situation] where all of the presidential candidates are satisfied."
Electoral Commission President Justice Ireen Mambilima said she was investigating complaints from both the PF and Mr Hichilima's United Democratic Alliance.
Mr Mwanawasa's victory came as Patriotic Front supporters battled riot police for a second day in several districts of Lusaka.
Protesters threw stones at police who responded with teargas and by firing live ammunition into the air.
Looting of shops owned by supporters of Mr Mwanawasa's Movement for Multiparty Democracy (MMD) has been reported in parts of Lusaka.
There has also been rioting in the northern city of Kitwe, the AFP news agency reported.
President Mwanawasa has won billions of dollars in debt relief
Clashes initially broke out on Sunday in the capital Lusaka when the electoral commission announced that Mr Sata had fallen from first place to third in interim vote counts.
The violence and allegations of irregularities contrast with the voting on Thursday, which international observers praised as being generally efficient and transparent.
Mr Mwanawasa is to be sworn in on Tuesday when results from parliamentary and local elections that were held with the presidential vote are expected to be announced.
Since being originally elected in 2001, Mr Mwanawasa has been credited with raising economic growth above 5% and winning Zambia billions of dollars of debt relief.
But the economic reforms have not improved life for most of Zambia's poor, revival in the crucial copper sector has been slow and unemployment is high.
Mr Mwanawasa's election victory in 2001 was also accompanied by allegations of fraud.