Nigerian President Goodluck Jonathan has declared a state of emergency in areas hard hit by violence blamed on the radical Islamist sect Boko Haram.

In an address on state television Saturday, Mr. Jonathan said the measure is in force in parts of Yobe and Borno states in the northeast, Plateau state in central Nigeria, and Niger state in the east.

He said a temporary closure of borders in those areas is needed to address security challenges and restore normalcy to the country.

The move came following a series of Christmas Day attacks in northeastern Nigeria, including four that killed about 40 people, most of them Christians.

The violence is blamed on Boko Haram, an Islamist sect that has claimed responsibility for multiple bombings and shootings in the north and in the capital, Abuja. The group's name means “western education is a sin.”

The violence is raising fears that the militants are trying to ignite sectarian strife.

The opposition has criticized the Jonathan administration for failing to control Boko Haram.

Nigeria is roughly divided into a mostly Muslim north and a predominantly Christian south.