MANAMA, Bahrain — In a dark alleyway of a low-slung suburb here, two dozen protesters gathered quietly and prepared to march toward a United States naval base. A teenager wrapped his scarf close to his mouth, bracing for tear gas. A man peeked out of his doorway, holding his infant daughter above his head, to show her a ritual of defiance that has become a grinding way of life.

For months, the protests have aimed at the ruling monarchy, but recently they have focused on a new target. To their familiar slogans — demanding freedoms, praising God and cursing the ruling family — the young protesters added a new demand, written on a placard in English, so the Americans might see: “U.S.A. Stop arming the killers.”

Thousands of Bahrainis rose up 16 months ago, demanding political liberties, social equality and an end to corruption. But the Sunni monarchy, seen by the United States and Saudi Arabia as a strategic ally and as a bulwark against Iran, was never left to face the rage on its own.

More than a thousand Saudi troops helped put down the uprising and remain in Bahrain, making it a virtual protectorate. The United States, a sometimes critical but ultimately unshakable friend, has called for political reform but strengthened its support for the government. Last month, the Obama administration resumed arms sales here.