January 19, 2010 11:47 a.m. EST

STORY HIGHLIGHTS

• Activist says at least 70 people killed and about 600 injured in violence
• Violence prompted imposition of a curfew Tuesday
• Hundreds have died in decade of Christian and Muslim clashes in region

Lagos, Nigeria (CNN) — Authorities have slapped a curfew on a city that has seen repeated violence between Christians and Muslims in Nigeria, but it has failed to stop the latest outbreak of killing, officials told CNN.

A local activist said at least 70 people had been killed and about 600 injured in the most recent outbreak.

The violence broke out Sunday and flared up again Tuesday, prompting the imposition of a curfew through Wednesday, a local official said.

But the curfew has already been broken and there have been “a number of casualties,” said Gyang Choji, special advisor on religious affairs to the governor of Plateau state.

Sani Shehu of the Civil Rights Congress in Jos said thousands of people had been displaced and were sheltering in military and police headquarters. There was no independent confirmation of Shehu’s figures.

It is not clear what sparked the latest round of violence, but hundreds have died in clashes between Christians and Muslims in central Plateau state in the past decade.

In November 2008, at least 700 Nigerians died in Christian-Muslim riots that followed a disputed local election, Human Rights Watch reported.

The most populous country in Africa, with a population of more than 150 million, Nigeria is almost evenly divided between Muslims and Christians.

With more than 78 million Muslims, it is has the sixth largest Islamic population in the world, according to a study last year by the Pew Forum on Religion & Public Life.

It has become the focal point of Christian and Muslim groups — in Nigeria and abroad, said Eliza Griswold, who has spent the last five years traveling to Nigeria to examine the causes of religious violence.

“Nigeria has become a battleground state for Christians and Muslims around the world who see themselves involved in a numbers game,” said Griswold, author of “The Tenth Parallel,” an upcoming book that explores the tension between Christians and Muslims just north of the equator in Africa and Asia.

“Any Christian or Muslim who has the point of view that numbers matter has a stake in Nigeria,” she said.

The divisions between Christianity and Islam are more than symbolic in Nigeria. There’s a geographic boundary: Nigerian Muslims tend to live in north, while Christians live in the south, Griswold said.

“There is this attitude that Islam is under siege by the Christian West and, by proxy, Nigerian Christians,” she said. “There is this sense among some devoted Muslims in the north that we need to be part of the larger Islamic community, and we need to prove that we belong.”