(CNN)At least 3.7 million people, including world leaders, marched in anti-terrorism rallies in Paris and elsewhere in France on Sunday, French officials said, calling the massive gathering in the nation's capital the largest in France's history. The day was emotional and peaceful, a gesture of unity just days after Islamic extremists slaughtered 17 people. World leaders joined French President Francois Hollande, including British Prime Minister David Cameron, German Chancellor Angela Merkel and Spanish Prime Minister Mariano Rajoy. The day also brought together an unlikely duo at the rally: Palestinian Authority President Mahmoud Abbas and Israeli Prime Minister Benjamin Netanyahu.
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NYPD and other U.S. law enforcement alerted to threat from ISIS
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Massive crowd at anti-terrorism rally in Paris was the largest in French history, French Mission to U.N. says
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Many world leaders present, but Obama, Kerry, Holder not at rally to represent U.S.
Sunday brought the end to a traumatic week in @placeholder.
NYPD employees were told to "remain alert and consider tactics at all times while on patrol," especially in light of the attacks in @placeholder last week, in an internal memo.