"This is a serious violation of the ceasefire," military spokesman Brigadier Daya Ratnayake said of the reported recruitment of children in Sri Lanka's volatile east. Child recruitment is banned under the February 2002 ceasefire, which ended fighting in a two-decade civil war between the government and the Tigers.
Mr Ratnayake said the rebels had taken five boys, aged 13 to 15, against their parents' wishes, and that two 17-year-old girls were also abducted on their way to a church.
The brigadier said the families had complained to the military and police, who have informed the European teams monitoring the ceasefire. Monitors confirmed an increase in complaints about child recruitment by the Tigers.
"There has been a steady increase of complaints in July, particularly in the Batticaloa district," said Helen Olafsdottir, a spokeswoman for the monitors.
Mr Ratnayake said all the abducted teenagers had been in school, and the rebels had stepped up child recruitment in response to serious problems within their ranks, including many desertions.
The accusations came amid reports that the guerrillas had returned five underage combatants to their parents and 15 others to an education centre in the past week.
The guerrillas began fighting in 1983 for an independent state for the country's minority ethnic Tamils, who claim discrimination by the majority Sinhalese.
About 65,000 people were killed in the conflict before the government and rebels signed the ceasefire, brokered by Norway.
Subsequent peace talks have stalled because of disagreements about how much autonomy the Tigers should have.