Ceasefire monitors in Sri Lanka are investigating the killing of 13 Tamils near the northern town of Jaffna.
Scenes of grief as relatives mourn those killed
A four-year-old boy and a baby were among those shot dead on Saturday night on the navy-controlled island of Kayts.
"There are lots of questions as to who could have been behind this," the monitors' spokeswoman told the BBC.
Tamil Tiger rebels have accused the navy of "slaughter". The authorities deny the charge and have blamed the rebels for the killings.
Last week, the monitors repeated that they had evidence to suggest the authorities were involved in killing Tamils, although not in a systematic way.
In the latest incident, they say they are "not ready to make any assumptions".
"Most of the people dying are civilians who are being threatened by different factions," Sri Lanka Monitoring Mission spokeswoman Helen Olafsdottir told the BBC.
"What appears to be tit for tat from both sides is having a negative impact on the ground."
Shot while asleep
Residents on Kayts say they heard gunshots on Saturday night coming from where navy sailors were camping.
The Liberation Tigers of Tamil Eelam (LTTE) website said nine people were killed in the village of Allaipiddy, having gathered in the same house for safety. Three others were killed in nearby Velanai and one in Vangalady.
The Allaipiddy victims included a boy of four and his four-month-old brother, who were shot as they slept alongside their parents.
The Tigers say the navy or paramilitary groups supported by the security forces killed the Tamils.
The navy has denied any involvement. A government statement condemned the killings and suggested instead they could have been the work of the rebels.
"Minister Keheliya Rambukwella, spokesman on security matters, said the ruthless killing of Tamil civilians could very well be a part of the LTTE strategy to divert international opinion," the statement said.
The rebels say they have no access to the area.
The Scandinavian-led ceasefire monitors have urged both sides in the increasingly bloody conflict to observe a 2002 truce accord, which is under severe strain but is still technically in place.
More than 200 people have been killed within the Tamil and Sinhalese communities in the past month, many of them members of the security forces or civilians.