Sri Lanka's Tamil Tiger rebels have increased their numbers of child soldiers in spite of a ceasefire, the United Nations says.
The Tigers had pledged to end child recruitment
The UN's children's agency, Unicef, has urged the rebels to release about 1,300 children in the Tamil Tiger ranks.
The Tigers dispute the figures, saying the great majority of those counted as children by Unicef are over 18.
The BBC's Frances Harrison in Colombo says there is the real possibility that the child soldiers may fight again.
Twice this week the Tigers have warned the ceasefire could break down because of problems with the peace process.
Unicef on Thursday appealed to the Tamil Tigers to release the child soldiers it says they are holding.
The figure of 1,300 child soldiers was given in a report on child recruitment in 2003.
The report says the Tigers recruited more than 700 child soldiers last year, the youngest being just 10 years old.
Under the terms of Sri Lanka's two-year-old ceasefire, the Tigers can still recruit adult fighters.
But they have made several commitments not to take anyone under 18-years of age.
Our correspondent says that has been repeatedly flouted - with reports of school children being bundled into vans and driven away by the rebels.
Later on Thursday the Tamil Tigers said Unicef's figures on child soldiers were inaccurate.
A spokesman told the BBC Tamil service that the names submitted to the Tigers by Unicef, only 138 of them had birth certificates showing them to be under 18-years-of age.
The Tigers say they do not accept recruits without birth certificates.
The spokesman, Dayamaster, said the Tigers' leadership had promised to examine the cases of the 138 fighters under 18.
Centre almost empty
Last year Unicef and the Tamil Tigers agreed an action plan to rehabilitate child soldiers.
There was much media interest in children freed in October
However, it is not being expanded as planned because so few children have been released by the rebels to the project.
A transit centre opened by Unicef in rebel territory last October to process released child soldiers now stands almost empty.
The centre only received 55 children in three months and most have been sent back to their parents or sent to live in children's homes.
Unicef says that until it sees a much greater level of commitment from the Tigers to releasing child soldiers, it will not open a second transit centre in the east of the island.
Our correspondent says it is clear the entire project is in jeopardy if the Tigers do not show they are serious about addressing the issue.
There is growing concern about the future of the Sri Lankan peace process.
On the government's side it has been led by Prime Minister Ranil Wickramasinghe who came to power on a pledge to end two decades of ethnic conflict.
But his moves towards the rebels have been consistently criticised by President Chandrika Kumaratunga.
Their differences erupted in November when President Kumaratunga dismissed three of his ministers and took direct control of the defence portfolio.
Since then the peace process has been stalled.
On Thursday, the Tigers said they would stay away from a conference of international aid donors because of the power struggle between the prime minister and the president.
The Tigers were invited to attend the aid talks - scheduled to take place on Friday - by Yasushi Akashi, a special envoy from Japan, the biggest of Sri Lanka's donor nations.
A statement on the pro-Tamil website, Tamilnet.com, quoted the Tigers' political leader, SP Thamilselvan, as saying their participation in the aid talks at this stage would sow "doubts in the minds of the Tamil people".