BANGKOK, Thailand -- Children are being snatched off the streets of Myanmar and forced to fight and commit atrocities in an army with the world's largest number of boy soldiers, according to human rights investigators.

A report released Tuesday by Human Rights Watch claims that as many as 70,000 soldiers in Myanmar's national army were under 18, with the vast majority forcibly conscripted.

Myanmar, also known as Burma, fields an army of some 350,000 to fight a variety of ethnic minority groups that also reportedly recruit boys into their ranks.

"To be a boy in Burma today means facing the constant risk of being picked up off the street, forced to commit atrocities against villagers, and never seeing your family again," the New York group said in the report.

Myanmar denied the allegations.

"The government finds it very difficult to understand on what basis it is making such claims, saying that 20 percent of the national army is made up of underage children," it said in a statement.

The human rights group said the report drew on interviews with current and former child soldiers to examine recruitment by the army and 19 opposition groups.

The report said recruiters for the army apprehend boys at bus and train stations, markets and other public places, threatening them with jail if they refuse to join.

Recruits are allegedly sent to camps where they undergo weapons training, are routinely beaten and brutally punished or killed if they attempt to escape.

Boys as young as 12 are sent into combat and forced to commit abuses against civilians, rounding up villagers for forced labor, burning villages and carrying out executions, according to Human Rights Watch.

The report quotes one 14-year-old boy who said the army conscripted his 11-year-old friend, who was beaten by guards for crying because he didn't get enough food.

Another boy soldier described how his unit rounded up 15 women and children, shooting the mothers and beating babies to death against rocks. He was 13 at the time, the report said.

Children are also found in the ranks of rebel groups, some of which have long been fighting for greater autonomy from the central government.

The United Wa State Army, known for involvement in drug trafficking, has the largest number of boy soldiers while the Kachin Independence Army also recruits girls, the report found.

Youngsters are also enlisted in forces of the Karen, Shan and Karenni rebels, although the three have official policies against recruiting anyone under 18.

One rebel group, the Karen National Union, says it takes in orphans but denies using child soldiers in combat. "We don't give them military training. Our policy is not to let the children soldiers fight," Mahnshar Laphan, the group's general secretary, said in an interview.

In early 2001, two 12-year-old twins, Luther and Johnny Htu, sought refuge in Thailand after leading a rebel band of Karens known as God's Army.

Myanmar leads the world in the number of boy soldiers because the army has difficulty finding adult recruits and desertion rates are high in a force that has doubled since 1988, said Jo Becker, the children's rights advocacy director for Human Rights Watch.

The Coalition to Stop the Use of Child Soldiers last year estimated that more than 300,000 children were fighting as soldiers in 41 countries.

The London-based coalition said the children, about 120,000 of them in African armies, were used as front-line fighters, minesweepers, spies, porters and sex slaves.

International law prohibits recruiting children under the age of 15, while several United Nations conventions condemn the practice of having anyone under 18 serve as a soldier.