They said the pre-dawn explosions on Monday were the latest of a string of sporadic bombings in the southern Ain al-Hilwah refugee camp.
No one was reported injured in the camp, which is controlled by Palestinian factions and which Lebanese authorities do not enter.
The camp has been the scene of tensions between Islamist activists and loyalists of Palestinian President Yasir Arafat's Fatah faction.
A bomb targeted the camp's Fatah office in January, while a second hit a residential area.
The two sides clashed in May last year for control of the camp. Seven people were killed in those battles.
Lebanese politicians hostile to 390,000 Palestinian refugees registered in a dozen camps across Lebanon, have pointed to Ain al-Hilwah as a haven for militants and organised crime.
But officials in Beirut and Palestinian leaders say the refugees live in desperate conditions because Israel refuses to let them return home.