Start here: The fight against ISIS on Friday

(CNN)From Iraq to Syria to Egypt, Europe and beyond, the ISIS threat -- and the fight against it -- is spreading.

In Iraq, planning for a ground offensive against ISIS appears to be underway. In London, officials are frantically trying to track down three teenage girls believed to be on their way to life with ISIS in Syria. And in the United States, officials warn of ISIS efforts to recruit more young people to join the fight.
CNN is tracking the story around the globe. Here's the latest reporting on the jihadist group and the global efforts to stop it:

    THE MOSUL ATTACK PLAN

    Key battlegrounds in fight against ISIS
    Key battlegrounds in fight against ISIS

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      Key battlegrounds in fight against ISIS

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    Key battlegrounds in fight against ISIS 01:56
    Up to 25,000 Iraqi troops: 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, or Kurdish, 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?

    THE THREAT

    Minnesota teen charged with trying to join ISIS
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      Minnesota teen charged with trying to join ISIS

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    Minnesota teen charged with trying to join ISIS 02:06
    Minnesota arrest: Federal authorities on Thursday charged a 19-year-old Minnesota man on suspicion of trying to travel to Syria to join ISIS. Hamza Naj Ahmed, charged with attempting to provide material support to ISIS, is accused of traveling to New York's John F. Kennedy International Airport with the intent of flying to Istanbul, Turkey, in November. Investigators were tracking him because he was communicating with a Minneapolis man who has been overseas and is suspected of extremist ties, a federal law enforcement official familiar with the probe said. In other recent cases, authorities have arrested an Illinois teenager and three Colorado teenage girls, accusing them of attempting to travel to the Mideast to join ISIS.
    Mother: My son went to Syria to help women and children
    Mother: My son went to Syria to help women and children

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      Mother: My son went to Syria to help women and children

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    Mother: My son went to Syria to help women and children 03:12
    Canadian mother's fight: After her son left life in Canada to die fighting for ISIS in Syria, Christianne Boudreau is lending her voice to two organizations trying to combat radicalization by ISIS recruiters. "It's so easy for them to get to our children, to access our children," she said. "We need to start arming ourselves with the knowledge, the awareness, the education, and to be able to deal with these issues and be able to speak with our children at an early age."
    London teens may headed to Syria: Police in London say three teenage girls are missing from their homes and may be making their way to Syria. The girls, two of them 15 and one 16, have not been seen since Tuesday when, police say, they took a flight to Istanbul.
    Expert: ISIS believes terror is their 'sacred duty'
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    Expert: ISIS believes terror is their 'sacred duty' 04:50
    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 independently to confirm the account.

    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.
    Suicide car bombings: The Libyan branch of ISIS, which calls itself Wilayat al-Barqa, claimed responsibility for three simultaneous suicide car bomb explosions in the Libyan city of Gobba, in a posting on ISIS' online media forum. Friday's blasts killed at least 30 people and injured more than 40 others, said Maher Shami, head of the Libyan House of Representatives' Media Office.
    Iraqi envoy says ISIS may be harvesting victims' organs
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    Iraqi envoy says ISIS may be harvesting victims' organs 01:55
    Harvesting organs: Iraq's U.N. ambassador says his country has asked the United Nations to look into another shocking allegation -- that ISIS is harvesting organs from slain civilians and selling the body parts. Britain's ambassador to the United Nations, Mark Lyall Grant, said there was no proof or evidence of the claim.

    THE COUNTEROFFENSIVE

    Is ISIS shifting its focus to Libya?
    Is ISIS shifting its focus to Libya?

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      Is ISIS shifting its focus to Libya?

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    Is ISIS shifting its focus to Libya? 01:48
    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 is asking that a U.N.-imposed arms embargo be lifted so it can better fight the threat.
    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.
    Secret U.S. 'hit list' of ISIS suspects revealed
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      Secret U.S. 'hit list' of ISIS suspects revealed

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    Secret U.S. 'hit list' of ISIS suspects revealed 02:48

    THE SUMMIT

    Denying legitimacy: The United States is not at war with Islam but with "people who have perverted Islam," President Barack Obama said this week at his three-day Summit on Countering Violent Extremism.
    Obama: 'We are not at war with Islam'
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      Obama: 'We are not at war with Islam'

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    Obama: 'We are not at war with Islam' 03:32
    The White House has gone out of its way not to name Islamic extremism as the summit's central focus. Obama explained why. Groups such as ISIS, he said, are "desperate for legitimacy."

    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 killer 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.