(CNN) -- At the start of Syria's civil unrest, Omar would rally against the government alongside his schoolmates, later taking to the streets in his hometown of Salqin.
Two years later, at the age of 14, he became a child soldier, training to join the ranks of rebel group Jabhat al-Nusra. He learned how to use weapons, make bombs and use mines. But when it came to fighting on the front line, he was scared.
"Then our sheikh came to encourage us to go fight and gave us speeches about jihad," Omar told Human Rights Watch. "So after two days, I went to front line."
Omar is just one of many boys being used on the battlefield in Syria's civil war, according to an HRW report released Monday. Many are forced to fight in battle. Others must act as snipers, man checkpoints, spy on opposing forces or carry out other, equally dangerous tasks.
Amr, 17, told Human Rights Watch that he first joined the Daoud Brigade, an Islamist rebel group, when he was 15. He later agreed to sign up for a suicide attack mission, feeling socially pressured to sign the volunteer list. Other children had also signed on, he said.
With Syria entering its fourth year of civil war, grim accounts of child soldiers being used on the battlefield are now emerging. Though the specific number of child fighters in Syria is unknown, the Violations Documenting Center, a Syrian monitoring group, has documented 194 deaths of "non-civilian" male children since 2011.
Of the 25 boys interviewed by HRW for the report, many reported joining opposition forces simply to follow a relative or friend. Others become opposition fighters because of circumstance -- living in battle zones or suffering at the hands of government forces.
The report demands the discharge of all soldiers under the age of 18 in Syria and warns anyone backing such organizations of being potentially complicit in war crimes.
It also accuses the Islamic State in Iraq and Syria, a powerful jihadist group, of recruiting children through free schooling campaigns.
Pro-government militias were not investigated in the HRW report, which cited logistical and security concerns.
Enlisting anyone under age 18 in armed conflict is a violation of international law.