JOHANNESBURG — The International Criminal Court's prosecutor on Tuesday condemned the escalation of "appalling levels of violence" in Nigeria's northeastern Islamic uprising and warned she would prosecute members of any party most responsible for war crimes and crimes against humanity.

Prosecutor Fatou Bensouda said her office is continuing a preliminary examination into allegations that Boko Haram extremists are killing large numbers of civilians, using girls and boys to participate in the conflict and forcing massive numbers of people from their homes.

She also warned Nigeria's government of its obligation to prosecute crimes that "deeply shock the conscience of humanity."

"No one should doubt my resolve, if need be, to prosecute those individuals most responsible for war crimes or crimes against humanity," Bensouda said in a statement from the court's headquarters in The Hague.

Both Boko Haram and the Nigerian military are accused of summary executions of hundreds of civilians in the 5-year uprising that killed more than 10,000 people last year.

Boko Haram has increased the ferocity, deadliness and tempo of its attacks in recent weeks, with international outrage over reports as many as 2,000 civilians may have been systematically slaughtered in a Jan. 3 attack on the town and military base at Baga, on the border with Cameroon.

Boko Haram also has increased attacks on neighboring Cameroon, realizing fears that the conflict is spreading. Boko Haram is holding a large swath of northeast Nigeria and declared it is recreating an ancient Islamic caliphate that included parts of Cameroon, Chad and Niger.

Niger's foreign minister, Bazoum Mohamed, told a meeting Tuesday of the Economic Community of West African States to discuss a collective response to Boko Haram that Nigeria's home-grown militants no longer are a Nigerian problem but threaten the security of the region.

Chad sent troops Sunday to fight Boko Haram in northern Cameroon, and Cameroon said Tuesday more than 10,000 of its citizens are fleeing border regions following cross-border attacks.

The International Organization of Migration said Tuesday more than 1 million people are displaced in northeast Nigeria. More than 100,000 have fled to Niger, threatening a regional humanitarian crisis.