Johannesburg - Zambia's opposition leader Michael Sata on Tuesday again rejected ruling party Rupiah Banda's victory in last week's presidential by-election, setting the stage for a protracted political stand-off in the southern African country.

"I have not lost this election," Sata, 71, told South Africa's SAfm radio. "Rupiah Banda has no vision, Rupiah Banda has no platform. The only platform Rupiah Banda is on is cheating."

Sata's Patriotic Front planned to turn to the courts Tuesday to challenge Banda's slight edge over the populist opposition leader in Thursday's vote.

Banda, also 71, was sworn in Sunday as president to serve the remaining three years in the second term of popular deceased leader Levy Mwanawasa. Mwanawasa died in August after suffering a stroke.

The Electoral Commission of Zambia said the centrist, ex-diplomat Banda won 40.09 per cent of the votes cast, against 38.13 per cent for the populist Sata.

Sata, who was also defeated in presidential elections in 2001 and 2006, alleges the election was fraudulent, claiming among other things that voting continued in some places while the first results were being announced.

Two African election observer teams, however, gave the election a clean bill of health.

The Zambian army and police have been on alert since last week for post-election violence, but only minor rioting in parts of the capital Lusaka and the Copperbelt mining region were reported at the weekend.

In 2006, Sata's initial refusal to accept his defeat at the hands of Mwanawasa sparked a week of rioting, mainly in Lusaka.

Zambia is Africa's largest copper producer but 65 per cent of the population of over 11 million still live on less than a dollar a day.

Banda has promised to continue Mwanawasa's prudent economic policies, which won over foreign investors and donors. (dpa)