BAGHDAD -- The Sunni protest movement here is turning increasingly violent, freshening memories of the brutal sectarian conflict of 2006 and raising troubling parallels to the Syrian civil war.
It has also highlighted an uncomfortable reality for American diplomats here who are scrambling to contain the crisis: at the core of Sunni grievances is a set of laws and practices imposed by the United States in the earliest days of the occupation.
The results of those policies, particularly a set of antiterrorism measures, are visible today throughout the country. Informants who once helped the American military now do the same work for the Iraqi government, sometimes putting innocent people in prison. Thousands of detainees, rounded up in terrorism sweeps, languish in prisons for years without being charged.
And former officers of Saddam Hussein's military, banished by the Americans under their "de-Baathification" policy and later promised by the Iraqis the chance to return and regain their salaries and social status, remain on the outside looking in.
When Sunnis began protesting around the country in December, they put a list of demands to the government: release detainees, reform the use of confidential informants and put an end to rules denying former Baath Party members -- most of them Sunnis -- jobs and pensions.
At the heart of the troubles are the antiterrorism tactics, which have been continued by the current Shiite-led government, often casting a wide net around Sunnis, ensnaring the innocent and guilty alike.
Often, Sunni critics say, the roundups are based on false information provided by informants who are far from disinterested observers.
"The security forces don't ask me to make up stories, but I know informants who do because they want more money," said a man in Baquba who works as an informant and who gave only his first name, Ghalib. He said he made $600 from the Americans for tips that led to arrests, and now makes just $100 per arrest from the Iraqis.
Another informant in Baquba, who also worked for the Americans and gave his name as Abu Basim, said he often informs on people he believes only "sympathize with extremists." He said that "many innocent people" have been convicted based on his intelligence, and that sometimes government officials have encouraged him to provide false information to secure arrests.
Sunni resentments have been festering since 2003, when the Americans arrived, instantly upending the old social and political order and turning millions of Sunnis, especially those with ties to the old leadership, into society's outcasts.
Consider the trajectory of Khalid al-Obaidi's life: The son of an army general under Mr. Hussein who later became an officer himself, Mr. Obaidi lived a life of privilege.
"We had servants, a driver, a chef," he said in a recent interview. "They treated sons of officers in a special way. We had a special house. We had our own social club."
Now, banished from the armed forces, he earns a living driving a taxi cab, is close to being evicted from his small rental apartment and worries how he will pay for a decent education for his children. His neighborhood in Baghdad, once a well-tended enclave for army officers, is now neglected and strewn with trash.
But last year, he learned from a television news program that the government was inviting former officers to return. "I was so happy," he said. "It was the best news I had heard in a long time."
So far, the promise is unfulfilled. At least five times he has visited a local army office to apply for reinstatement, and each time, he says, "We'd wait in line for hours before someone would say, 'Come back another day.' "
Mr. Obaidi had been willing to give democracy a try in the 2010 national elections, after joining large numbers of Sunnis in boycotting previous votes. Now, he said, "I will not vote again."
Perhaps more ominous for the future stability of Iraq, Mr. Obaidi, like many other ordinary Sunni citizens, is not only fed up with politics but is sympathetic with those who have recently taken up arms against the government.
The change of heart followed a raid by government forces on a Sunni protest camp in Hawija, a northern village near Kirkuk, that left nearly 50 people dead. "They should defend themselves," he said. The government, he said, "is pushing us to fight to maintain our life."
When the protests began the government seemed to acknowledge the legitimacy of some of the demands, and formed a committee under a deputy prime minister, Hussein al-Shahristani, to address them. The committee quickly announced the release of a number of detainees and said it was preparing new policies on the use of secret informants and the de-Baathification law.
But critics have said that many of the detainees who were said to be released are still in prison, and they dismissed the other planned changes as empty promises. Human Rights Watch recently complained of a lack of transparency in the process, saying, "It is unclear whether any of the promises have been carried out."
Mr. Shahristani, in response to the criticism, said in an interview: "We have done what we thought was necessary. Has it satisfied all the demonstrators? No."
Now, Iraqis on both sides of the divide say the chance to quell Sunni anger by revising these practices seems to have been lost. Sunni protesters have symbolically set fire to their list of demands. Shiite leaders say reconciliation is politically impossible, given the sectarian polarization set off by the recent violence here and the continuing civil war in Syria, which is increasingly aggravating the region's sectarian fault lines.
"To be realistic, in the current environment, there is no support for this," said Sami al-Askari, a Shiite member of Parliament who is close to the prime minister, Nuri Kamal al-Maliki. "This is the impact of Syria. The whole region is talking about clashes between Sunnis and Shiites."
Something greater seems to have been lost here, some Iraqis say, the dream of a sectarian coexistence in which disagreements are contested through politics. The prospect for political blocs comprising Sunnis and Shiites to emerge in advance of next year's national elections, as they did before the previous vote in 2010, seems far-fetched.
"The Shiite feeling is that they are under threat," Mr. Askari said. "The Sunnis feel like they are marginalized. In this environment, it is madness to say, 'I have a list of Sunnis and Shiites and people will vote for it.' "
Yasir Ghazi contributed reporting from Baghdad, and an employee of The New York Times from Baquba, Iraq.
This article originally appeared in The New York Times.