JOS, Nigeria -- Two car bombs exploded at a bustling bus terminal and market in the central Nigerian city of Jos on Tuesday, killing at least 118 people and wounding dozens, police said.

There was no immediate claim of responsibility for the twin car bombs, but they bore the hallmarks of Boko Haram, an Islamist extremist group.

The second blast happened half an hour after the first, killing some of the rescue workers who had rushed to the scene.

Dozens of bodies and body parts were covered in grain that had been loaded in the second car bomb, witnesses said. A Terminus Market official said he helped remove 50 dead or injured people. He spoke on condition of anonymity because he is not allowed to give information to reporters.

"It's horrifying, terrible," said Mark Lipdo of the Stefanos Foundation, a Christian charity based in Jos.

At least 118 people were killed, the National Emergency Management Agency said. Coordinator Mohammed Abdulsalam said fires were still raging in buildings, and he expected to find more bodies after firefighters got them under control.

Tensions have been rising between Christians and Muslims in the city, the capital of Plateau state in Nigeria's Middle Belt region that divides the country into the predominantly Muslim north and Christian south. It is a flash point for religious violence.

Boko Haram has claimed other recent bomb attacks, including two separate bomb blasts in April that killed more than 120 people and wounded more than 200 in Abuja, the nation's capital. One bomb went off at a busy bus station.

Lipdo said said a white van that held the first bomb that went off Tuesday was parked for hours in the marketplace, raising suspicions of vendors and others who reported it to the authorities, but nothing was done.

He said authorities also had another warning of impending violence: A man with explosives strapped to his body was arrested Saturday and told police that many militants had been ordered to plant bombs around churches and public areas in Jos.

President Goodluck Jonathan extended sympathy to affected families and "assures all Nigerians that government remains fully committed to winning the war against terror, and this administration will not be cowed by the atrocities of enemies of human progress and civilization," a statement said.

The Nigerian government and military's failure to curtail the 5-year-old Islamic uprising, highlighted by the mass abduction of nearly 300 schoolgirls and lack of progress in rescuing them more than a month later, has caused national and international anger.

Jonathan has been forced to accept help from several nations including Britain and the United States in the hunt for the girls, who were taken in northeast Nigeria.

The extremist group is demanding the release of detained insurgents in exchange for the girls -- a swap officials have said the government will not consider. The extremists are threatening to sell the girls into slavery if Jonathan does not free the detainees.

Diplomats said Nigeria on Tuesday asked a U.N. Security Council committee monitoring sanctions against al-Qaida to add Boko Haram to the list, with an arms embargo and asset freeze.

Boko Haram wants to turn Nigeria into an Islamic state under Shariah law. Half of Nigeria's population of 170 million is Christian, as is most of the population of Jos.

More than 300 people have been killed in assaults on towns and villages in recent weeks, and the extremists were blamed for an attack on a Chinese camp in neighboring Cameroon last week in which one Cameroonian soldier was killed and 10 Chinese workers abducted.

The militants have been attacking with increasing frequency despite a year-old military state of emergency in three of Nigeria's states to curtail the uprising.

The Senate on Tuesday voted to extend the emergency for another six months but only if Jonathan devotes more money to the military campaign and to better arming demoralized soldiers who say Boko Haram is better equipped. A letter with the conditions was sent to the president.

More than 2,000 people have been killed in the insurgency this year in Africa's most populous nation, compared with an estimated 3,600 between 2010 and 2013.

Information for this article was contributed by Andrew Drake and Edith M. Lederer of The Associated Press.

A Section on 05/21/2014