21 people have been killed in a shooting in Nigeria. That's according to the Red Cross, which says fresh attacks on Christians in the country's northeast have heightened fears of a sectarian conflict.

The shooting took place in a hall on Friday, where a group of Christians had gathered. They were mourning the deaths of those killed in an attack the previous day.

Witnesses claim most of the deceased were Christians. And in another part of the country, Maiduguri, a Christian couple was shot dead.

A Nigerian newspaper published a warning from an Islamic movement, called Boko Haram, earlier this week. It said Christians in Muslim-majority areas in northern Nigeria had three days to leave or else they would be killed.