For all of its international influence, ISU is close to weightless on the scale of financial heft.

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"Every effort should be made to get a second resolution passed that would approve a full-scale monitoring mission and, simultaneously, influence all groups in Syria without exception into cooperating for the sake of implementing the Annan plan, " Russian Foreign Minister Sergei Lavrov said at a news conference Friday in Moscow.

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Friday's letters appear to be the first large-scale effort by members of the Senate to influence the president's decision.

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