(CNN) -- The Christmas Eve attacks in the volatile Nigerian city of Jos have claimed at least 31 lives, a bloody aftermath in a region long torn by Christian and Muslim hostility.
Gyang Choji, a special adviser to the governor of the west African country's Plateau state, confirmed the death toll on Saturday, and said 74 others were wounded.
Most of the injured have serious wounds, and some of them suffered leg amputations.
Seven blasts rippled through the city as residents celebrated Chrismas Eve, four in the Kabong area and three in Angwa Rubuka. Choji cited a "lapse in security" by a special task force not "doing what they were expected to do."
"Five different bombs blasts in the heart of Jos. This is the height of insecurity in this city," Choji said.
Most of the injured have serious wounds; some of them got both legs amputated and the authorities are concerned about their conditions.
Choji said no one has claimed responsibility but Islamic fundamentalists are suspected of carrying out the attacks.
"For long, they have been threatening to use violence against Christians and free the region from the shackles of Western imperialism," Choji said.
The Jos region lies on a faith-based fault line between Muslim-dominated northern Nigeria and the mainly Christian south.
On March 7, at least 200 Christians villagers were massacred near Jos, and more than 150 Muslims were killed in an attack in a nearby town, Kuru Karama, on January 19.
Hassan John, a Jos resident and journalist with the media department of the Anglican Diocese of Jos, described a scene of chaos in what was expected to be a joyous Christmas Eve.
He had just come out of church about 7 p.m., when he heard the sound of the first explosion. He rushed to the site, which he described as a beer parlor frequented by locals.
"By the time I got there, there were women crying, people screaming. It was all chaos, people were screaming, blood everywhere."
"I counted eight corpses all over, seven in the building," John said. A second blast went off within a couple of minutes after the first one.
John said residents, especially young men, became agitated over the lack of security in what has been a volatile area.
"Soldiers fired a couple of rounds into the air because a riot was developing," John said.
Choji, who is special adviser on religious affairs to the governor, said it was unclear who set off the blasts or whether they were related. But the bombs detonated in the "same manner," Choji said, and they "all went to where people were concentrated."
In recent weeks, the governor's office had received letters purported to be from some Muslim organizations threatening attacks against Christians, Choji said.
"The security officials didn't take the threat letters seriously. They were thought of as gimmicks, and at the end of the day, they became reality."
A special task force sent to Plateau state by the federal government in the preceding two days had gone on radio telling residents to go about their business and not to worry about the security situation in the area, Choji said.
The government had increased security and checkpoints throughout the past week, including additional patrols in various areas of Jos, Choji said.
In Nigeria, Africa's most populous nation, more than 13,500 people have died in religious or ethnic clashes since the end of military rule in 1999, the Human Rights Watch said in a report earlier this year.
There have been other deadly sectarian clashes in Nigeria over the years, including one outbreak in Jos in September 2001 that left about 1,000 dead, the Human Rights Watch said.
CNN's Mila Sanina, Giang Nguyen and Joe Sterling contributed to this report