BBC News with Sue Montgomery

The Nigerian President Goodluck Jonathan has declared a state of emergency in some parts of the country following a series of bomb attacks on Christmas Day. The Islamist group Boko Haram said it carried them out. President Jonathan has described the group as a "

cancerous

" growth attempting to destroy Nigeria. Tomi Oladipo reports from Lagos.

In a live address to the nation, President Goodluck Jonathan declared a state of emergency in some areas in the north of the country, which have become scenes of violence. The president also announced that the borders of these states would be closed to prevent what he described as terrorist elements from getting in. A special military unit will also be

set up

under the chief of defence staff to overcome the security challenges. President Jonathan has been

under increasing pressure

to address the violence that has

plagued

many parts of northern Nigeria, and this announcement reveals his toughest stance so far.

The army in South Sudan says 6,000 warriors from the Lou Nuer tribe have attacked the town of Pibor - home to the rival Murle tribe. On Friday, the United Nations deployed more troops to Pibor, but there are reported to be only 800 soldiers defending the town. Thousands of people had already fled Pibor. Here's our East Africa correspondent Will Ross.

South Sudan's army spokesman Colonel Philip Aguer told the BBC that thousands of armed men from the Lou Nuer tribe entered Pibor town and set fire to the grass-