BEIRUT—A car bomb killed a prominent politician opposed to Hezbollah, drawing Lebanon deeper into the sectarian morass of Syria's civil war and harking back to a spate of earlier assassinations blamed on Damascus and its Lebanese allies.

The blast in central Beirut on Friday killed six people including Mohamad Chatah, a moderate aligned with Lebanon's main Western-leaning political bloc, the Future Movement. The Lebanese Red Cross said 15 people were critically wounded.

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