DEARBORN, Mich. — Twice recently, vandals have shattered windows at three mosques and a dozen businesses popular among Shiite Muslims along Warren Avenue, the spine of the Arab community here. Although the police have arrested no one, most in Dearborn's Iraqi Shiite community blame the Sunni Muslims. "The Shiites were very happy that they killed Saddam, but the Sunnis were in tears," Aqeel Al-Tamimi, 34, an immigrant Iraqi truck driver and a Shiite, said as he ate roasted chicken and flatbread at Al-Akashi restaurant, one of the establishments damaged over the city line in Detroit. "These people look at us like we sold our country to America." Escalating tensions between Sunnis and Shiites across the Middle East are rippling through some American Muslim communities, and have been blamed for events including vandalism and student confrontations. Political splits between those for and against the American invasion of Iraq fuel some of the animosity, but it is also a fight among Muslims about who represents Islam. Long before the vandalism in Dearborn and Detroit, feuds had been simmering on some college campuses. Some Shiite students said they had faced repeated discrimination, like being formally barred by the Sunni-dominated Muslim Student Association from leading prayers. At numerous universities, Shiite students have broken away from the association, which has dozens of chapters nationwide, to form their own groups. "A microcosm of what is happening in Iraq happened in New Jersey because people couldn't put aside their differences," said Sami Elmansoury, a Sunni Muslim and former vice president of the Islamic Society at Rutgers University, where there has been a sharp dispute. Though the war in Iraq is one crucial cause, some students and experts on sectarianism also attribute the fissure to the significant growth in the Muslim American population over the past few decades. Before, most major cities had only one mosque and everyone was forced to get along. Now, some Muslim communities are so large that the majority Sunnis and minority Shiites maintain their own mosques, schools and social clubs. Many Muslim students first meet someone from the other branch of their faith at college. The Shiites constitute some 15 percent of the world's more than 1.3 billion Muslims, and are believed to be proportionally represented among America's estimated six million Muslims. Sectarian tensions mushroomed during the current Muslim month of Muharram. The first 10 days ended on Tuesday with Ashura, the day when Shiites commemorate the death of Hussein, who was the grandson of the Prophet Mohammad and who was killed during the bloody seventh-century disputes over who would rule the faithful, a schism that gave birth to the Sunni and Shiite factions. The Shiites and the Sunnis part company over who has the right to rule and interpret scripture. Shiites hold that only descendants of Mohammad can be infallible and hence should rule. Sunnis allow a broader group, as long as there is consensus among religious scholars. Many Shiites mark Ashura with mourning processions that include self-flagellation or rhythmic chest beating, echoing the suffering of the seventh-century Hussein. As several thousand Shiites marched up Park Avenue in Manhattan on Jan. 28 to mark Ashura, the march's organizers handed out a flier describing his killing as "the first major terrorist act." Sunnis often decry Ashura marches as a barbaric, infidel practice.