As Iraqis awoke Sunday to the news that American forces had finally and completely left their country after nearly nine tumultuous years, their feelings of relief were chilled by an unmistakable sense of menace.

A deepening political crisis that pits the country’s Shiite prime minister against some of his most outspoken Sunni coalition partners is already raising fears that a brewing conflict could plunge the country into a new era of instability.

The crisis flared after the Shiite-dominated government of Prime Minister Nouri al-Maliki leaked plans Saturday to arrest a Sunni official, Vice President Tariq al-Hashimi, on charges of terrorism. Hashimi’s mostly Sunni Iraqiya bloc responded by announcing a boycott of the national parliament.

Frantic telephone calls involving President Jalal Talabani, Maliki, Sunni politicians and U.S. Embassy officials appeared to resolve the issue. A judicial committee was formed to “thoroughly investigate” the terrorism charges, a solution that seemed to allow time for negotiations to unfold.

But on Sunday, tensions soared again when Maliki asked parliament to hold a no-confidence vote that would enable him to dismiss another top Sunni official, Deputy Prime Minister Saleh al-Mutlak.

Mutlak says he is certain that the move springs from comments he made in a CNN interview last week calling Maliki the “biggest dictator ever.” He says that he stands by the comment, and that the boycott will be upheld until Maliki takes steps to fully share power with his Sunni partners in Iraq’s coalition government.

Hashimi and Mutlak flew to Kurdistan on Sunday night, ostensibly to seek the intervention of Kurdish leaders but inevitably fueling speculation that they were seeking refuge.

While similar disputes have erupted in the past, only to be smoothed over by lengthy negotiations, this one seemed in the minds of many ordinary Iraqis to acquire ominous overtones in the wake of the departure of the Americans. There have been more soldiers and armored vehicles on the streets of Baghdad in recent days, they say. Tanks have been deployed outside the homes of Hashimi, Mutlak and a third Sunni politician, their guns pointed toward their gates. A convoy of trucks laden with ammunition queued for access to the fortified Green Zone on Sunday, adding to the jittery mood.

The crisis is dividing Iraq along sectarian lines, threatening a revival of the tensions that erupted in widespread bloodletting in the middle of the past decade. Sunnis detect a plot by Maliki to crush his rivals and cement his authority now that U.S. forces have departed. Shiites think that Hashimi and other Sunni politicians may be behind some of the acts of terrorism that have abated but not disappeared from Baghdad’s streets.

“I think there’s going to be a coup,” said Muwafak Mohammed Ali, 47, voicing one of the many theories swirling as the long-simmering feuds among politicians erupted into full view even before the last convoy of American soldiers crossed the border into Kuwait early Sunday morning. He wasn’t sure by whom.

“This is Iraq. It is what happens,” said Ali, a wedding musician who lives near the Green Zone. “It will be by the military or one of the political parties.”

“I don’t think the Americans should have gone,” he added. “The situation isn’t stable.”

Fears of oppression

U.S. officials had warned ahead of their departure that Iraq would face challenges once they left. The commander of U.S. forces in Iraq, Gen. Lloyd J. Austin III, cautioned at last week’s ceremonies marking the end of the war that Iraq’s future would depend on whether its leaders made “the right choices, basing their decisions on what is best for the Iraqi people.”

But the speed with which leaders are turning on one another has compounded fears that they won’t make those choices.

“It’s all making me very nervous,” said Bashar al-Mandalawi, an Iraqi journalist who said he is thinking about relocating his family to northern Kurdistan.

He suspects the political furor will die down, but a bigger concern, he said, is the future of personal freedoms in a country where Shiite religious parties, led, for now, by Maliki’s Dawa Party, appear to be tightening their control. “These religious parties want to take us back to the earliest days of Islam,” he said. “They are going to oppress independent people who don’t want Iraq to be close to Iran.”

Fears of an expansion of Iranian influence are widespread among Sunnis and Shiites. Ali, the wedding musician, said that he fears a future in which his livelihood is wiped out by prohibitions on partying, music and dancing, and that the Americans had helped check Iranian influences on the Iraqi government and moderate the behavior of the politicians.

“The Americans were controlling things somewhat,” he said.

No celebration, for now

Most Iraqis say they are glad the Americans are gone, if only out of bitterness for the bloodshed their presence helped cause. But even in their absence, the troops were prying open the sectarian divide, with Shiites more inclined to be joyful than Sunnis.

The withdrawal coincides with the holy month of Moharram, a period when Shiites mourn the martyrdom of one of their holiest figures, Imam Hussein, at the hands of a Sunni army nearly 1,400 years ago, when the schism between the two branches of Islam was born. Baghdad is ablaze with green, black and red flags commemorating Hussein’s death, heightening a growing sense of encirclement by many Sunnis who once thought they were the majority in this ancient capital.

All forms of celebration are forbidden during Moharram, and that is the reason why festivities have not been held to mark the exit of U.S. forces, said Jabbar Jodi, director of the National Theater, who is planning a program of dance and music to mark the departure in January. He gestured to a photograph hanging on the wall of himself and Maliki — “I love him so much” — alongside pictures of other politicians who have visited the theater.

One nail was empty — the picture had been taken down that day. He pulled it out of his desk drawer with a grin. It was of him and Hashimi. “Because of the situation,” he explained wryly before burying it back in the drawer.

Special correspondents Asaad Majeed and Aziz Alwan contributed to this report.