Sri Lanka has stepped up security for a contentious weekend ceremony marking 15 years since the end of the nation's long civil war and thousands of civilians were killed in the conflict's final offensive.
Public events celebrating the Tamil Tigers separatist group -- which fought a no-holds-barred battle to establish an ethnic minority homeland -- are illegal and authorities have prevented the staging of past memorials.
Sri Lanka's Tamils say the events are held to remember all victims of the decades-long war, which concluded in 2009 after a military offensive in the last Tiger stronghold condemned internationally for the indiscriminate bombardment of civilians.
This year's commemoration will be attended by Amnesty International's global chief Agnes Callamard, the most senior foreign dignitary so far to attend a remembrance event in the island nation's battle-scarred north.
"Security forces and the police are on alert for any trouble during this period," a top police official told AFP late Thursday, declining to be named.
Police said they had information that Tamils were planning to use the occasion to commemorate Tiger guerrillas and had obtained court orders preventing any illegal remembrance.
This week police arrested four people in the Tamil-majority north for distributing porridge in memory of those killed in the war.
The meal was a staple during periods of the war when government forces were besieging Tamil communities, and it was also customarily distributed to Tiger soldiers before they went to battle.
- 'Heavy surveillance' -
Tamil residents near the ceremony site told AFP that security forces had been noticeably more active in their communities as the anniversary neared.
"There is heavy surveillance of the people, and it is intimidation," one Tamil resident said, asking not to be named for fear of retribution.
May 18 marks 15 years since the killing of the Tamil Tigers' charismatic but reclusive leader Velupillai Prabhakaran, who had led the separatist group in open rebellion against Sri Lankan forces since the 1970s.
His death in the village of Mullivaikkal was the culmination of a lightning military offensive that killed at least 40,000 civilians in the final months of the fighting, according to UN estimates.
Sri Lankan forces were accused of indiscriminately shelling civilians after telling them to move to "no fire zones" to clear the path of their assault.
Amnesty chief Callamard arrived in Colombo on Thursday for talks with Sri Lankan leaders including President Ranil Wickremesinghe.
The rights watchdog for years has pressed for Sri Lankan authorities, who have repeatedly refused to permit an international probe into wartime atrocities, to properly investigate and prosecute those responsible for abuses.
Callamard will be joining "thousands of war-affected Tamils who will be commemorating all those lost to the Sri Lankan civil war at an event in Mullivaikkal", her office said.