Nigerian President Goodluck Jonathan has made a surprise visit to northeastern Borno state, the center of the Boko Haram insurgency.
Jonathan, who is campaigning for re-election, flew to the state capital of Maiduguri on Thursday. There, he spoke to troops at an army barracks and met with hundreds of civilians displaced from Baga, a town captured by the insurgents earlier this month.
The president has been criticized for not doing enough to push back the insurgents or to recover more than 200 schoolgirls kidnapped by Boko Haram last April.
Related TV report by Mariama Diallo:
The group has killed thousands of people and seized large parts of Borno state despite a state of emergency Jonathan declared there and in two neighboring states in May 2013.
U.S. Secretary of State John Kerry said recent Boko Haram attacks in northeastern Nigeria were "nothing less" than a crime against humanity.
Kerry spoke Thursday during a visit to Bulgaria, a day after Amnesty International released satellite images said to show widespread destruction caused by Boko Haram fighters in two towns this month.
"It's an enormously horrendous slaughter of innocent people, and Boko Haram continues to present a serious threat not just to Nigeria and the region but to all of our values and to all of our sense of responsibility regarding terrorism," Kerry stated.
Kerry called Boko Haram "one of the most evil and threatening terrorist entities on the planet today."
He also said he discussed a possible initiative on Nigeria and Boko Haram with British Foreign Secretary Phillip Hammond, but did not give further details.
Amnesty International released before-and-after satellite images of Baga and nearby Doron Baga that it says show an estimated 3,700 structures were burned down soon after Boko Haram seized control of Baga on January 3.
The human rights group said interviews with witnesses and local officials suggest that the militants shot hundreds of civilians, including small children and a woman who was in labor.
Nigeria's military put the death toll from the Baga attacks at 150 but local officials have said it is likely above 1,000.
Amnesty said Wednesday that based on its research, Boko Haram may have attacked Baga because it was home to members of the Civilian Joint Task Force, a group of people helping the army fight the Islamist militants.
The Nigerian army has struggled to contain Boko Haram, which now controls large areas of Borno and seized a key base from the military in Baga in the January 3 attacks.
The group has said it is taking territory for a caliphate ruled by Islamic law.
Boko Haram's dominance in the northeast and the ongoing violence have raised doubts about whether voting for next month's presidential election can take place in Borno and two neighboring states.
Jonathan is facing what appears to be a strong challenge from a new coalition of opposition parties and their presidential candidate, former military leader Muhammadu Buhari.