Mr. Frankel cited reports that the guerrillas had attacked civilians, backed up by independent rights groups, and said removing their posts was meant to curb their ability to organize or encourage violence.

The bans are the latest sign of Facebook’s growing power in many countries, where its control over the flow of information and public discourse makes it akin to national broadcaster, public utility and political regulator all rolled into one.

And they are the latest test of Facebook’s ability to wield that power responsibly.

But Facebook’s intervention has brought unintended consequences that have troubled humanitarian groups and conflict experts in Myanmar.

The bans, they say, have swept up pages crucial for protecting some of the country’s most vulnerable communities. And some worry that they will further tilt control of information about the conflict toward the military, which rights groups consider to be guilty of far graver atrocities than the rebels.

Senator Edward J. Markey, Democrat of Massachusetts, sent a letter to Facebook saying he was “deeply troubled” by the bans. He called the groups’ Facebook presence “important to broader efforts at a lasting peace” and warned that their removal would disrupt efforts by humanitarian groups and by international conflict observers, “including the United States.”

Ms. Khon Ja, crediting the platform’s reach in Myanmar’s conflict zones with helping to save lives, said, “Facebook is very important for us.” Without pages like that of the Ta’ang rebels, she worried, it could become harder to shield civilians from violence.