At least four people are dead in the latest wave of violence to sweep Nigeria.

Authorities say all four victims were killed Friday night in two attacks on outdoor beer motorcycle gunmen.

In one attack, in Yola in Adamawa state, the gunmen pulled up to the beer garden and opened fire, killing two patrons and injuring one police officer.

The other attack took place in Gombe, the capital of Gombe state.  Officials there said the gunmen pulled up on a motorcycle and started firing, killing two people and injuring a third.

Officials have yet to identify the suspects, but the attack took place just days after the militant group Boko Haram promised more attacks.

Nigerian authorities blame Boko Haram for hundreds of deaths in bombings and shootings over the past 18 months.  The group has claimed responsibility for several of the attacks, including a Christmas Day bombing of a church near Abuja that killed more than 30 people.

The group is believed to want wider implementation of sharia, or Islamic law, across Nigeria.  It recently warned Christians in Muslim-majority northern Nigeria to leave the area.

U.N. Human Rights chief Navi Pillay on Thursday called on Nigerian political and religious leaders to conduct joint efforts to halt sectarian violence in the country.

Pillay said it is especially important for Muslim and Christian leaders to "condemn all violence," including retaliatory attacks.  She said those efforts could help stop a dangerous situation from "spiraling out of control.

In response to the violence, President Goodluck Jonathan recently declared a state of emergency in 15 areas.

The president has also deployed extra troops to the north, but attacks have continued.

Some information for this report was provided by AP, AFP and Reuters.