Rival supporters in Sierra Leone fought with sticks and stones on Thursday, adding to fears that the build-up to next week's presidential run-off could reopen wounds from the civil war.

Dozens of youths stoned a convoy of the opposition All People's Congress (APC) as it rolled into the southeastern town of Segbwema. They then fought with the party's guards before police dispersed them with tear gas, a Reuters reporter said.

APC leader Ernest Bai Koroma, who came first in an August 11 poll with 44%, faces Vice-president Solomon Berewa of the ruling Sierra Leone People's Party (SLPP), who won 38%.

Koroma's APC is in a strong position because of backing from SLPP dissident Charles Margai and his PMDC party, which has created an opposition majority in the new parliament. There is a split between the APC-leaning north and SLPP south.

The election is the first in the former British colony since United Nations (UN) peacekeepers left two years ago after helping end the 1991-2002 civil war.

The pro-SLPP youths forced Koroma's campaign convoy to turn back from Segbwema, near the border with Liberia. The local SLPP party headquarters was set ablaze in the violence.

President Ahmad Tejan Kabbah said this week he could declare a state of emergency if electoral violence worsened.

Police imposed a brief curfew on Monday in the eastern border region, a centre of the illegal diamond mining trade which fuelled the civil war.

UN Secretary-General Ban Ki-moon was "concerned about the tensions and violence that have been increasing in Sierra Leone since last week", his spokesperson said on Wednesday.

"He calls on all parties and their leaders to do everything necessary to prevent the situation from escalating."

VOLATILE EX-COMBATANTS

More than 70 000 fighters were disarmed at the end of the war, each given the equivalent of $100 to hand in their guns. Many drifted into driving motorcycle taxis after donor-funded skills' training schemes closed down or ran out of money.

Mustapha Sesay and Femi Rashid are former foes who work together in a motorcycle taxi club that brings together ex-combatants in the southern town of Bo.

"I shoot you like a chicken," laughs Sesay, 22, an ex-rebel child soldier. "You don't know how to fight," retorts Rashid, 40, once a traditional Kamajor hunter who battled rebels.

The Bo Bike Riders' Association, where the pair work, represents nearly 5 000 motorcycle taxi drivers throughout southern Sierra Leone.

"Once they were fighting, and now they are working together ... It is wonderful," said David Ngombu from international aid organisation Conciliation Resources.

Sesay, who was abducted to fight by rebels when he was 12, says he will not go back to war.

"We only fight with this now," he said, pointing to his thumb, which illiterate voters use to mark their ballot choice.