Start here: Latest developments in the fight against ISIS

(CNN)ISIS ups the ante on its savagery. Iraq asks U.N. to look into organ-harvesting allegations. And U.S. President Barack Obama wants to deny the militants legitimacy.

Here's the latest on the jihadist group and the global efforts to stop it:

THE BRUTALITY

    Burned alive: Every few days, it seems as though ISIS ups the ante on its savagery. Wednesday brought news that the militants killed at least 40 police officers and tribesmen in a town they recently seized in Iraq's Anbar province -- and that most of the victims were burned to death. That's according to an Iraqi official. CNN hasn't independently confirmed the account. The Pentagon says it's looking into it.
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    Harvesting organs: Iraq's U.N. ambassador says his country has asked the U.N. to look into another shocking allegation -- that ISIS is harvesting organs from slain civilians and selling the body parts. Britain's ambassador to the U.N., Mark Lyall Grant, said there was no proof or evidence of the claim.
    Iraqi envoy says ISIS may be harvesting victims' organs
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    THE THREAT

    Turkish warning: Turkey's intelligence agency has warned police that ISIS members may be planning attacks in Ankara and Istanbul against the diplomatic missions of countries in the U.S.-led coalition, the national newspaper Hurriyet reported. Militants have crossed into Turkey after retreating from the Syrian city of Kobani, the warning by the National Intelligence Organization reportedly said. CNN is trying to independently confirm the account.

    THE COUNTEROFFENSIVE

    Plan of attack: An Iraqi ground offensive to push ISIS out of Mosul is now expected to begin in April or May, a U.S. military official said Thursday. Up to 25,000 Iraqi troops could be involved, the official said. The attack will include five Iraqi army brigades that will be trained by the United States and Peshmerga forces that will try to cut off any ISIS escape routes north and west of the city, the official said. ISIS seized Mosul, Iraq's second largest city, in June. There's one big question lingering: What role, if any, could U.S. troops play on the ground as Iraqi forces try to retake it?
    End the embargo: ISIS is metastasizing at warp speed in Libya. The killings of 21 Egyptian Christians in Libya highlight how the group is taking advantage of the collapsing state. Now, Libya's asking that a U.N.-imposed arms embargo be lifted so it can better fight the threat.
    Is ISIS in control of affiliates in Libya and Syria?
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    Kill list: The United States is maintaining a list of about two dozen top ISIS operatives in Iraq and Syria that it hopes to target in airstrikes, a senior U.S. official said. No. 1 on the list? ISIS leader Abu Bakr al-Baghdadi.
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    THE SUMMIT

    Denying legitimacy: The U.S. is not at war with Islam but with "people who have perverted Islam," Obama said Wednesday at his three-day Summit on Countering Violent Extremism. The White House has gone out of its way not to name Islamic extremism as the summit's central focus. Obama explained why. Groups like ISIS, he said, are "desperate for legitimacy."
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    THE PROPAGANDA

    Speech analysis: Just as it's doing with "Jihadi John," the intelligence community is trying to figure out the identity of the new English-speaking executioner in the video ISIS released showing the beheadings of the Egyptian Christians. The most intriguing clue is in his voice: The accent appears to be either American or Canadian.