(CNN) -- Syria's major opposition group condemned Bashar al-Assad's regime Wednesday for "brutal massacres" this week and urged the U.N. Security Council to protect civilians against "acts of genocide." "The regime is using children as human shields so that tanks and armored vehicles can storm residential areas," said the Syrian National Council, which said that about 250 people have died over a 48-hour period. "Incidents of gruesome murders have been recorded," the council said Wednesday, including the killings of four brothers and the beheading of a sheikh, whose head was hung above a mosque entrance. Both incidents occurred in Idlib, and the council says "acts of genocide" are occurring in Zawiyah Mountain in Idlib province in the northwest and the city of Homs in the west.
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NEW: Syrian opposition reaches out to international powers
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The United Nations estimates that about 5,000 people have died in Syrian violence this year
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The Syrian National Council wants U.N. and Arab League action
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It says nearly 250 civilians died over a two-day period
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