Campaigning for the election is in full swing
United Nations Secretary General Ban Ki-moon has expressed alarm at the violence surrounding the run-up to Sri Lanka's presidential election.
He has urged all political parties and their supporters to "refrain from violence... and to avoid provocative acts throughout the election period".
At least four people have been killed in poll-related violence in the weeks leading up to the election.
The 26 January vote is taking place amid heightened tension.
Gen Sarath Fonseka, Sri Lanka's former army chief is the main rival to President Mahinda Rajapaksa.
He resigned from his post as chief of defence staff in November following differences with the government over who should take credit for defeating the Tamil Tiger rebels last May.
"The secretary general is concerned about the growing violence in the lead-up to the presidential election in Sri Lanka, including the reported killing of political activists," a UN statement said.
Sri Lankan groups monitoring the presidential election campaign say the levels of election-related violence and misuse of state resources are at their worst for at least 20 years.
Scores of people have also been wounded in the violence, with more than 20 instances of firearms used or deployed as a threat, Rajith Keerthi Tennakoon, of the Campaign for Free and Fair Elections, told the BBC's Charles Haviland in Colombo.
He said he believed both sides were "aggressively moving towards a violent election" and he feared it would worsen.
The Sri Lankan army defeated the Tamil Tiger rebels last May, ending 26 years of civil war.
The rebels were fighting for a separate Tamil homeland.