GUMMI, Nigeria — Lawali Isa brandishes the stump where his right hand was amputated on the orders of an Islamic court.
"This is how justice was done to me," said Mr. Isa, who had the penalty administered by hospital surgeons in May after being convicted of stealing two bicycles. "Now I would prefer to die rather than live."
In the 20 months since a dozen northern Nigerian states started imposing the strict edicts of Islamic law, or Shariah, one man is appealing a sentence of death by stoning, a handful of petty crooks have had their hands amputated and a few accused adulterers, including a 17-year-old girl who said she was raped, have been flogged.
There has been a greater, and deadlier, result: Muslim-Christian tensions have exploded in the north of Africa's most populous country, fueling violence that has killed thousands and wrecked neighborhoods, villages and cities.
Islam and Christianity had coexisted relatively peacefully for more than a century in Nigeria and other parts of Africa, where fundamentalism is rare and many adherents of both religions mix in elements of animism and ancestor worship.
In Nigeria, Muslim women have a liberal interpretation of the Islamic dress code, wearing a brilliantly colored veil that is often draped casually over their head instead of covering the face.
Men wear brightly colored clothes, in contrast to the austere customs of Muslims in the Middle East.
Shariah's backers here defend the harsh punishments as a deterrent to crime in a dangerous land.
Mr. Isa, who says he stole car parts and broke into homes for more than 15 years, admits the only reason he "repented my ways" was because his hand was cut off. Now he sells firewood and candy from a tin-roofed mud home that he bought with money donated by people who took pity after the amputation. "I can never steal again without two hands," he said.
Shariah has few detractors in Mr. Isa's hometown of Gummi, a dusty farming community in the sweeping savannah emptiness of Zamfara, the northeastern Nigerian state that was the first to impose Islamic law, in January 2000.
The sleepy town has welcomed the break from crime that Shariah has brought.
But the overwhelming acceptance of Islamic law is due more to the fact that nearly everyone in Gummi — and the rest of Zamfara — is Muslim, with just a handful of Christian merchants who keep a low profile.
In northern cities where there are large Christian populations, Shariah has sporadically pitted young religious zealots against each other in blood baths. Strife in the hilltop city of Jos early last month killed 165 people by official count alone — hundreds more probably died.
Supporters of Shariah see it as a path to honesty and justice, fostering Muslim piety while allowing Christians to practice their religion as they wish. Only Muslims are supposed to be tried in Islamic courts, while Christians answer to secular courts.
To its opponents, Islamic law is a barbaric mingling of church and state, a fanatical mix that in some cases forbids all women to ride with men on motorcycles or bicycles — the main mode of transportation in the poor region — and bans social diversions like alcohol and fashion magazines.
At a recent gathering of a few dozen Christians in Zamfara's capital, Gusau, the Rev. Linus-Mary Awuhe, the priest at Our Lady of Fatima Catholic Church, spoke angry words of Christian fears about "Muslim supremacy."
"Even when nobody is dying on the streets, there is no peace. There is war in the hearts of people. That war waits for its time to break out," Fr. Awuhe said. "Christians will not fold their arms and be led to the slaughter like goats."
Nigeria's constitution has long permitted states to impose Islamic law on their Muslim citizens. But it was only after President Olusegun Obasanjo won the 1999 elections, ending 15 years of military dictatorship, that northern politicians began taking advantage of the provision.
Long-standing ethnic enmities between the mainly Muslim Hausas of the north and the southern Yorubas and Igbos, who are Christians and animists, have added to the divide.
But some Muslims and Christians believe party politics is behind the implementation of Shariah and the resulting violence.
Mr. Obasanjo's People's Democratic Party accuses the All People's Party, which governs Zamfara and many other northern state governments, of using Shariah selectively to target political enemies. Christian groups accuse Zamfara's government of using Shariah to favor Muslims in the granting of government contracts and loans.
"All of Islam favors Shariah, and that includes me," said Alhaji Umar Gwamna, a Muslim opposition leader who is chairman of Mr. Obasanjo's party in Gummi. "But this is not Shariah for everyone, it is a corrupt Shariah favoring those who are friends of the Zamfara state government."
Alhaji Umaru Danawu, a merchant and prominent supporter of the state government, answers that brothels, gambling houses and drinking places have disappeared since the adoption of Islamic law. Once-brazen robberies in the outdoor markets have become a rare occurrence, and "dens of vice" have been replaced by Islamic schools and health clinics, he adds.
"Anybody who says this is politics does not understand our religion," Mr. Danawu said. "This is about following Allah."