JOS, Nigeria - A radical Muslim sect has claimed responsibility for the Christmas Eve bombings and church attacks in Nigeria that killed at least 38 people, and the group threatened new attacks to avenge local violence against Muslims.

Religious fighting has left more than 500 people dead this year in the deeply divided region where Jos is located. Authorities had already blamed the Boko Haram group for some of the deaths Friday, but the online statement attributed to the group was the first solid connection between the violence in two cities.

"Therefore we will continue with our attacks on disbelievers and their allies and all those who help them," the statement said.

It was not immediately possible to contact members of the sect, which had not previously used the website where the statement appeared. The head of national police, Yemi Ajayi, also said Tuesday that authorities were still investigating.

Two bombs went off near a large market in Jos where people were doing last-minute Christmas shopping Friday. A third hit a mainly Christian area of Jos, while the fourth was near a road that leads to the city's main mosque.

Officials initially said that at least 32 died from the blasts, and police have not updated that figure publicly.

An official with the National Emergency Management Agency told journalists that he had counted 80 deaths, but the regional NEMA coordinator said only three hospitals were visited. It was not verified whether the patients counted were in fact blast victims, said the regional NEMA coordinator, Alhassan Aliyu Danjuma.

That same day, two churches were attacked in the northern city of Maiduguri about 320 miles away, killing at least six people. Nigerian authorities blamed Boko Haram, and said a Baptist pastor and two choir members preparing for a late-night carol service were among the victims.

The radical Muslim sect is also known by a much longer Arabic name, which means "the organization of followers of the teachings of Prophet Muhammad and champions of Islam and holy wars."