Norwegian mediators have asked both the Sri Lankan government and Tamil Tiger rebels to reiterate their commitment to the four-year-old ceasefire.
Relatives and friends mourn the family found hacked to death
It follows a breakdown in talks between the two sides in Oslo.
"We are in the deepest crisis in the peace process," Norway's top mediator, Erik Solheim said.
Meanwhile, four members of a family have been found hacked to death in the north west of Sri Lanka. The dead include two children.
The 30-year-old mother was found lying on the floor of her house in Vankalai, 15km (10 miles) from the town of Mannar.
There were signs that she had been sexually assaulted. The bodies of the father and two children were found hanging from the ceiling.
The Roman Catholic bishop in the area, Royappu Joseph, who visited the scene, told the BBC that some soldiers had visited the village earlier on Thursday, asking for information about locals.
The army has denied carrying out the killings and says the Tamil Tigers were to blame.
News of the latest killings came as a scheduled two days of talks in Oslo ended in recriminations.
The talks were due to focus on the security of European ceasefire monitors deployed in Sri Lanka.
But the rebels refused to meet Sri Lankan government representatives face-to-face, saying they would only talk to the Norwegians.
The EU last week branded the Tamil Tigers as terrorists
The two sides last met in February, but violence has since flared again. More than 300 people have been killed over the past two months.
Following the breakdown of Thursday's talks, the Norwegian mediators have written to both sides demanding a written response to questions relating to their commitment to the ceasefire.
They asked if the two sides were still committed to the ceasefire, whether they continued to want international truce monitors and whether they would guarantee their safety.
"The responses by the parties... will determine which steps will next have to be taken by the Norwegian government and the Sri Lanka Monitoring Mission, in close partnership with other actors in the international community," said a statement issued by the Norwegian government.
The BBC's Dumeetha Luthra in Colombo says the breakdown of talks is a serious setback for hopes of peace in Sri Lanka.
Erik Solheim says the peace talks are in their 'deepest crisis'
The Tamil Tigers are demanding that the European Union members withdraw from the peace monitoring mission in the country, responding to an EU decision to call the Tigers terrorists.
The majority of monitors are from member countries.
However, our correspondent says that finding other nations willing to take up the challenge is going to be next to impossible.
She says that if the Norwegian mediators' letter does not get the right answers, the international role in Sri Lanka's mounting conflict may be drawing to an end.
Meanwhile, the Sri Lankan government has heavily criticised the head of the monitoring mission, Ulf Henricsson.
It accused him of "disregard for the truth" because of a report in which the monitoring mission said both the government and the Tigers were responsible for the worsening violence.
This week's Oslo talks were called after a rebel attack last month on a navy convoy carrying the observers.