AMSTERDAM -- The prosecutor of the International Criminal Court says that after a preliminary investigation she believes that acts attributed to the Nigerian Islamist group Boko Haram are likely crimes against humanity.

"Information available provides a reasonable basis to believe that since July 2009 Boko Haram has launched a widespread and systematic attack that has resulted in the killing of more than 1,200 Christian and Muslim civilians in different locations throughout Nigeria," Fatou Bensouda wrote in a report issued Monday.

She said the potential crimes against humanity include murder and persecution. But she said she will only move to a full-fledged investigation after further study and depending on whether Nigerian authorities themselves are willing and able to prosecute "those who appear to bear the greatest responsibility."

Her report was based on evidence gathered through December 2012.

Nigeria declared a state of emergency on May 14 to fight an Islamic uprising by militants in the northeast who want to impose Islamic law across a country divided almost equally between the predominantly Muslim north and mainly Christian south.

Boko Haram's center of power is in the northeast, but last month Nigeria's army arrested 42 suspected Islamic extremists in the southwest states of Lagos and neighboring Ogun.

Bensouda noted that while that Nigerian government forces may also have violated human rights while conducting operations against Boko Haram, as of December 2012 there was no evidence they were targeting civilians.

The International Criminal Court is the world's permanent war crimes court, established in The Hague, Netherlands in 2002. The prosecutor's office formally launched its investigation into the situation in Nigeria in November 2010.

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  • A female student stands in a burnt classroom at Maiduguri Experimental School, a private nursery, primary and secondary school burnt by the Islamist group Boko Haram to keep children away from school in Maiduguri, northeastern Nigeria, May 12, 2012.(PIUS UTOMI EKPEI/AFP/GettyImages)

  • In a Sunday, Dec. 25, 2011 file photo, onlookers gather around a car destroyed in a blast next to St. Theresa Catholic Church in Madalla, Nigeria after an explosion ripped through a Catholic church during Christmas Mass near Nigeria's capital Sunday, killing scores of people, officials said. A radical Muslim sect, Boko Haram, claimed the attack and another bombing near a church in the restive city of Jos. (AP Photo/Sunday Aghaeze, File)

  • In a Sunday, Dec. 25, 2011 file photo, medical officials try to treat a victim of a bomb blast at a Catholic church near Nigeria's capital at Suleja General Hospital in Suleja, Nigeria. An explosion ripped through a Catholic church during Christmas Mass near Nigeria's capital Sunday, killing at least 25 people, officials said. A radical Muslim sect, Boko Haram, claimed the attack and another bombing near a church in the restive city of Jos. (AP Photo/Dele Jones, File)

  • This file image made available from Wednesday, Jan. 10, 2012, taken from video posted by Boko Haram sympathizers shows the leader of the radical Islamist sect Imam Abubakar Shekau. (AP Photo, File)

  • Bodies of people alleged to have been killed in a Friday attack on a town hall meeting of the Christian Igbo ethnic group lie on the floor in a hospital morgue in Mubi, in the Adamawa state of northern Nigeria, Saturday, Jan. 7, 2012. The town hall attack, which left at least 20 dead, is one of a string of deadly attacks claimed by radical Muslim sect Boko Haram. (AP Photo)

  • An anti bomb police officer collect soft drink can bombs recovered from islamic militants in Kano, Nigeria, on Tuesday, Jan. 24, 2012. Police said Tuesday that members of the radical Islamist group Boko Haram dressed in uniforms resembling those of soldiers and police officers when they launched their attack Friday in Kano. (AP Photo/Sunday Alamba)

  • In this Monday, Oct. 8, 2012 photo taken with a mobile phone, a police officer walks past a burnt out shopping mall in Maiduguri, Nigeria. (AP Photo/Abdulkareem Haruna)

  • In this frame grab from TV footage shot by the Nigeria television authority on Monday, Oct. 8, 2012 but aired Tuesday, Oct. 9, 2012, shows people lying down (condition of people unknown) on a street in Maiduguri, Nigeria. (AP Photo / Nigeria Television Authority)

  • A partially burnt down communication tower destroyed by Boko Haram in Maiduguri, Nigeria, Friday, Sept. 7, 2012. A radical Islamist sect claimed responsibility Friday for attacks on mobile phone towers which have crippled communications in Nigeria's northeast, as security forces struggling to control the violence said they had gunned down seven suspected sect members. (AP Photo/Haruna Umar)

  • Weapons and ammunition along with police uniforms and bulletproof vests recovered from suspected Boko Haram sect members, put on display in Bukavu Barracks in Kano, Nigeria, Wednesday, March. 21, 2012. (AP Photos/Salisu Rabiu)

  • Burnt our cars are seeing at the business and skills center following gun battle and explosions by the Boko Haram sect, in Potiskum, Nigeria, Saturday, Oct. 20, 2012. (AP/Photo Adamu Adamu)

  • Burnt out school block following a gun battle and explosions by the Boko Haram sect in Potiskum, Nigeria, Saturday, Oct. 20 , 2012. (AP Photo/Adamu Adamu)

  • In this Wednesday, March 21, 2012 file photo, suspected members of the radical Islamist sect Boko Haram, are detained by the military, in Bukavu Barracks in Kano state, Nigeria after an attack on a police headquarters, the home of a senior police officer and setting fire to a nearby bank. (AP Photos/Salisu Rabiu-file)