Gunmen open fire on a convoy of buses carrying minority Muslim voters in northwest Sri Lanka on Saturday, hours before polling in presidential elections.

There were no immediate reports of casualties, but a police official said the attackers had burnt tyres on the road and set up makeshift roadblocks to ambush the convoy of more than 100 vehicles.

"The gunmen opened fire and also pelted stones," a policeofficial said. "At least two buses were hit, but we have no reports ofcasualties."

Muslims from the coastal town of Puttalam were travelling tothe neighbouring district of Mannar, where they were registered to vote, thepolice official said.

Police reinforcements rushed to the area and cleared theobstructions on the road and escorted the convoy so that passengers could casttheir ballots.

The incident came as police and troops were locked in a tense standoff in the Tamil-dominated northern peninsula of Jaffna where residents complained of military roadblocks ahead of voting.

Police complained the incident to independent Election Commission that the army was illegally manning roadblocks that could discourage residents from casting their votes freely.

"After bringing to the notice of the army that the roadblocks were illegal at a time of a national election, they have dismantled them, "police said in a statement.

Police sources said they had also warned local militarycommanders that any disruption to the election would be reported to courts andoffenders prosecuted.

Sri Lanka's minority Tamils and Muslims were the deciding factors for the winning candidate in a close contest between the two front runners – housing minister Sajith Premadasa and the opposition's Gotabaya Rajapaksa.

Local media reports have feared that a strong military presence in Jaffna, the heartland of the island's Tamil minority, could influence voter turnout and favour Rajapaksa, a former defence ministry chief and brother of former president Mahinda Rajapaksa.