Recalling that local monitoring groups have reported numerous incidents of election-related violence, the New York based rights group called on Sri Lanka to "protect" voters.
"With evidence already of violence in the run-up to these elections, Sri Lankan authorities should take all necessary steps to protect voters and party supporters from attacks, threats, and intimidation," HRW said.
"The authorities should also ensure that voters can travel safely and securely to the polling booths and back."
The Centre for Monitoring Election Violence (CMEV), a longstanding independent monitoring organisation, documented 135 major incidents, 10 involving the use of firearms, and 624 minor incidents between July 13 and August 13, according to a report in Colombo Gazette.
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The major violations occurred mainly in Jaffna, Colombo, Batticaloa, and Gampaha districts. Three people have been reported killed and several injured, the report said.
However, another local monitoring group People's Action for Free and Fair Elections (PAFFREL) said the number of such incidents have been "very low" since July 13 till the campaign ended midnight last night.
There are three local monitoring groups, supplemented by international observers from the EU, Commonwealth Secretariat and the Asian Network of Election Monitors.
Shan Wijetunga of the Transparency International said that there will be more than 31,000 poll monitors in the election.
Over 15 million voters are expected to vote in 22 electoral districts to elect a 225-member parliament for a five-year term.