Security sources gave conflicting accounts of casualties, with one saying at least one person was killed and another saying only that one person was wounded.
Ambulances rushed to the scene and security personnel sealed off the area within a 200 metre (yard) radius of where the bomb exploded, in a stronghold of the Lebanese Shi'ite group Hezbollah.
Hamas officials in Beirut were not immediately available for comment.
Rocked since 2005 by assassinations and war, Lebanon has enjoyed greater stability of late and formed a unity government last month. It had spent months without a functioning government after June elections in which a Saudi- and U.S.-backed coalition defeated Hezbollah and its allies.
Several Palestinian militants and Hezbollah members have been killed in Lebanon in recent years in attacks their organisations have blamed on Israel.
Lebanon is home to 12 Palestinian refugee camps that house more than 200,000 registered refugees.
(Reporting by Mariam Karouny and Laila Bassam; Editing by Mark Trevelyan)
- Reuters - Thomson Reuters Foundation
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