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GENEVA -- The U.N.'s top human rights official is urging nations to immediately prevent more Syrian deaths and to relentlessly pursue justice for victims.

U.N. High Commissioner for Human Rights Navi Pillay say she is "appalled" by Syrian government attacks on civilians in the city of Homs.

She says there is an "extreme urgency for the international community to cut through the politics and take effective action to protect the Syrian population" in an 11-month-old uprising that has left more than 5,400 dead.

Pillay said Wednesday no statute of limitations exists for serious international crimes.

She promised "a sustained effort for as long as it takes to bring justice to all those who have been victims of the gross and systematic crimes taking place in Syria today."