The explosion gouged a crater in the pavement three feet deep and three feet across. The bomb, rigged from a gas cylinder attached to a bicycle, detonated at 1:45 in the afternoon, just as worshipers were leaving after Friday prayers at a Shiite mosque in Baquba, roughly 40 miles north of Baghdad. At least four people died and 32 were injured, police told NEWSWEEK. At the weekend the bomber had not been identified, but townspeople assume he was looking to spread distrust and anger between the Shiites and their predominantly Sunni neighbors. Police officials say the day's carnage could have been even worse if they hadn't found and defused a second bomb at another Shiite mosque a few miles away.

The sneak attacks keep coming--against both Iraqi civilians and Coalition forces. Last week's deadliest incident was the crash of a U.S. medical helicopter near Fallujah, killing all nine aboard. Witnesses said the Black Hawk was brought down by ground fire. Military spokesmen said an investigation was underway. Tuesday marks one month to the day of the capture of Saddam Hussein, humiliated and feeble, and Bush aides insist these are the death throes of the insurgency. And after more than 200 U.S. military deaths in Operation Iraqi Freedom, one more tragic attack can hardly alter the Pentagon's plans. Coalition control over Iraq's destiny--and its fractious ethnic and religious factions--is scheduled to end in less than six months, when the Coalition Provisional Authority (CPA) transfers power to an elected Iraqi leadership and disbands.

That thought scares Americans and Iraqis alike. Even if the transfer of authority allows GIs to step back from the front lines, deadly rivalries between Iraqis could make last week's bloodshed look like national unity. And an election-year U.S. troop drawdown is all but impossible. "If the Americans leave, there will definitely be a civil war," says Sheik Nadhim Khalil, 25, who has no great love for U.S. troops. In recent weeks they have ransacked his home and the mosque where he leads Friday services in Dholoiya, a farming town in the heart of the Sunni Triangle. U.S. officials think the best hope of preventing a bloodbath depends on creating an interim constitution that will somehow satisfy the demands of Iraq's disparate ethnic and religious groups. As if that alone didn't pose enough of a challenge, the deadline for producing the Transitional Administration Law is no later than Feb. 28.

America's head civilian in Iraq, L. Paul Bremer, has done everything he can to make it happen on schedule. He still needs a miracle. His biggest problem is the country's 4 million or so Kurds. With the help of U.S. air cover they broke free from Saddam Hussein's dictatorship in the wake of Operation Desert Storm in 1991. Since then a generation of Iraqi Kurds has grown up in a virtually independent state with its own laws, its own leaders and its own army. They don't want to trade their autonomy for life as an ethnic and religious minority in an overwhelmingly Arab nation of 25 million, including 15 million Shiites. On the contrary, the young Kurds are determined to reclaim an area that belonged to their people before the 1970s, when the Baghdad regime began a massive program of forced removals in and around the city of Kirkuk. The onetime Kurdish regional capital sits atop roughly 6 percent of the world's known oil reserves.

Last spring the Kurds' peshmerga fighters marched into Kirkuk with the 173d Airborne. Things turned ugly fast. Guerrilla units began sweeping through Kirkuk and villages south of the city, evicting nearly 2,000 Arabs. Ethnic clashes continued for a week until the Americans gained control. Some Kurdish militias were intercepted in the act of raiding Arab villages. Col. Bill Mayville, the 173d's brigade commander in Kirkuk, has been working ever since to mediate property disputes and organize peace talks with local Kurdish, Arab and Turkoman (ethnic Turk) leaders. He rolls his eyes at the Sunnis' constant allegations that he favors the Kurds. "We're in the middle, wearing a referee's jersey," he says. "The Kurds don't have Kirkuk."

Not yet, anyway. Mayville has repeatedly warned Kurdish leaders in the city to cool their superheated "Jerusalem of Kurdistan" rhetoric, and his troops have raided Kurdish political-party offices and confiscated AK-47s and rocket-propelled grenade launchers. "No party should have an RPG," says Emma Sky, the CPA's representative in Kirkuk. "What political activity requires an RPG?" Roughly 3,000 Arab and Turkoman protesters marched through the city on New Year's Eve, and a shoot-out erupted as they neared the Patriotic Union of Kurdistan headquarters. The clashes claimed four lives. No one seems to agree on who started it, but members of all three ethnic groups describe a succession of random shootings, explosions and kidnappings in the following days.

If the Kurds do secede, with or without Kirkuk, Bremer can scarcely hope to persuade other Iraqis to make sacrifices for the sake of national unity. Political observers quietly cheered when dozens of Sunni clerics gathered at Baghdad's Mother of All Battles Mosque on Christmas Day to form a consultative council, traditionally known as a shura. To outsiders the meeting looked as if the participants had finally decided to help build the new Iraq. But less than a week later one of the three organizers of the shura, Sheik Mehdi al Sumaidai, was arrested in a U.S. raid that turned up five sticks of plastic explosive, eight improvised grenades, 11 AK-47s and 3,500 rounds of ammunition, several RPG launchers and a training device for firing surface-to-air missiles at the Umm al Taboul (Mother of Drums) Mosque in the capital. Other shura members, denying any connection to the doings at the Umm al Taboul Mosque, insist their council is a legitimate political body.

Khalil, who made a quick trip from Dholoiya to Baghdad a few days after the raid, says he has joined the shura. If his attitude is any sign of what the group's members think, the cause of national unity is in deep trouble. Khalil makes no secret of his contempt for Iraq's Shiite majority. In his Friday sermons he has called for the creation of Sunni militias to challenge the Shiites' 10,000 or so Iranian-trained paramilitary fighters and the Kurds' roughly 70,000 battle-hardened peshmerga fighters. "We are willing to sacrifice our sons and fathers to stop the rule of black turbans," he says, using a Sunni term of disparagement for Shiites. "Being ruled by Shiites would be the same as being ruled by Iran. This is unacceptable." Attendance at his mosque has doubled in recent months.

Iraq's neighbors are saying prayers of their own as they watch what's happening next door. They have all had their share of ethnic problems with Kurds and other minorities, but their concern goes deeper than that. When the WMD searches came up empty, Bush aides began claiming that the invasion was actually a way of planting the seeds of democracy in Arab lands. Now the fear is that Iraq's collapse could destabilize the entire region.