(CNN) -- The Syrian government launched a major military operation Monday, sending thousands of troops into the town where the country's uprising began to carry out what witnesses described as a brutal, wider-scale crackdown. The United States threatened sanctions against the country, calling for a halt to Syria's "deplorable" actions. At the United Nations, a draft statement condemning the violence was being circulated among security council members, a U.N. diplomat said. Between 4,000 and 5,000 members of the Army and security forces equipped with tanks raided the southern city of Daraa just after 4 a.m. and began shooting indiscriminately, in some cases shooting into homes as people slept, according to an activist with the Syrian Observatory for Human Rights.
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NEW: The United States summons the Syrian ambassador in Washington
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Syria says Daraa citizens wanted the army to stop "terrorist groups"
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The United States is preparing new sanctions
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Syria reports "martyrs" killed and mutilated by "armed criminal groups"
Because @placeholder lies on the border, sealing it makes it difficult for besieged residents to flee the military offensive.