Soldiers detained Ahmad Jawabreh, 15, and Muhammad Eqtet, 16, after raiding their homes, popular committee spokesman Muhammad Awad told Ma'an.
Awad said a Molotov cocktail had been thrown at an army watchtower at the entrance to the town but caused no injuries.
A military spokeswoman said there were no arrests in Beit Ummar overnight.
She said three Palestinians were detained in Idhna, west of Hebron.
Meanwhile Yousef Abu Maria, a member of the national committee to resist the wall and settlements, said Israeli forces raided the Al-Mantara area. Soldiers fired stun grenades before entering homes, she added.