Lusaka - Police in the southern African country of Zambia were on high alert Wednesday as campaigning in a tense presidential election drew to a close amid signs of a possible dispute over the outcome.

The capital Lusaka was brought to a standstill as acting president Rupiah Banda, candidate of the ruling Movement for Multi-Party Democracy (MMD) and Michael Sata, leader of the main opposition Patriotic Front (PF) held their final rallies.

Sata, 71, drew a much bigger crowd at his than Banda, also 71, who is more popular in rural areas.

The populist Sata, who is promising more pro-poor policies and a greater stake for Zambians in the mining industry, used the occasion to cast Banda, a career diplomat who took over as president on the death of ex-leader Levy Mwanawasa in August, as corrupt.

At Banda's rally, which was broadcast on public television and radio, a number of leaders from other opposition parties not contesting the by-election were on hand to denigrate to Sata, who was defeated in 2001 and 2006, as dictatorial and thuggish.

Two other parties are also fielding candidates but the election is seen as a two-horse race.

Banda has campaigned on a theme of continuity with the popular Mwanawasa's prudent economic policies, which won over investors and donors. The election takes place against the backdrop of plummeting prices for copper - the country's biggest foreign exchange earner - on the back of slowing demand caused by slower global growth.

Only 3.9 million Zambians out of an estimated 11.7 million in total are registered to vote in the election, which observers fear might be characterized by the violence that gripped the 2006 election.

Sata, who is leading in two out of three polls, on Wednesday refuted allegations of inciting violence for warning he would not accept the outcome of the election if he suspected rigging.

In 2006, his initial refusal to accept his defeat at the hands of Mwanawasa sparked days of rioting.

Analysts say the mood will hinge on how the Electoral Commission of Zambia (ECZ) handles the results.

On Tuesday, police in the tourist capital Livingstone fired tear gas to disperse angry opposition PF supporters, who suspected that two trucks arriving from South Africa through the Zimbabwe-Zambia border were carrying pre-marked ballot papers. The ECZ said the trucks were carrying lamps and batteries for polling stations.

The opposition is distrustful of the MMD since a government- registered last month was discovered trying to illegally ferry unverified presidential ballot papers to a remote district. (dpa)