HONG KONG, Sept 4 (Reuters) - Hong Kong leader Carrie Lam on Wednesday announced the formal withdrawal of a controversial extradition bill that has plunged the Chinese-ruled city into its worst political crisis in decades.

The bill, which would have allowed extraditions to mainland China where courts are controlled by the Communist Party, triggered months of unrest and posed the gravest challenge to Chinese leader Xi Jinping since he came to power in 2012.

(Reporting By Hong Kong bureau)

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