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.


Backed by powerful allies, the government has pursued reform on its own terms. Dialogue between the country’s Shiite majority and the king has stopped. Twenty-one of the most prominent dissidents still languish in prison, and no senior officials have been convicted of crimes, including dozens of killings, that occurred during the crackdown last year. Opposition activists are still regularly detained or interrogated for their words.


On Friday, in what activists called a dangerous escalation, riot police officers forcefully dispersed a rally by Bahrain’s largest opposition party, injuring its leader. Every night, protesters march and clashes erupt, in a violent standoff that often seems a breath away from an explosion.


Some Bahrainis had pinned hopes for reconciliation on a report, issued six months ago, that investigated the events of February and March 2011 and found that the security forces had used indiscriminate force and torture in putting down the uprising. King Hamad bin Isa al-Khalifa promised to heed the report’s findings and punish officials responsible for abuse.


Government officials assert that reforms are bearing fruit, that a new special unit is investigating allegations of abuse, and that thousands of people who lost their jobs because they participated in the revolt or were accused of sympathizing with it have been rehired. Foreign advisers have been hired to overhaul the security services.


The justice minister, Khalid bin Ali al-Khalifa, said the polarization in Bahrain had not “reached a dangerous level yet.”


“It reaches a dangerous level when you don’t have a government in place,” he said, warning also about the increased used of incendiary devices by some protesters. “Many of the people are getting along with each other.”


John F. Timoney, a former Philadelphia and Miami police chief who was hired to help reform a Bahraini police force implicated in torture and killings, said that new curriculums were being taught at the police academy and that police stations were being fitted with cameras to prevent torture during investigations. He also said that the current climate could overwhelm his efforts.


“It’s a heavy lift, changing the culture,” he said. “If there’s no political solution here, it’s all for naught.”


The possibility of a solution seems remote. Opposition groups and human rights activists say that the reforms leave the state’s undemocratic core intact, and that they fail to address central grievances like corruption and the institutionalized discrimination against the Shiite majority.