The "Muslim Youth" group reportedly stated that it was launching a battle to "purge the Ain al-Hilweh camp of apostates."
The meeting in the Gaza Strip came amid mounting tensions between the Fatah-dominated Palestinian Authority and PIJ.
The outlook for unity on the ground among the Palestinians remains grim, and that is not necessarily a positive sign for Israel.
The mutual accusations came amid growing discontent in the Gaza Strip with Hamas over its failure to improve the living conditions of its residents.
The fighting has leaked out of the camp with shells falling on locations in Sidon.
While much is made of the antisemitic hatred produced by Hamas, it is easy to forget about the Palestinian Authority and Mahmoud Abbas' ruling party, Fatah.
Their fundamental disagreement is over the strategy for achieving their common purpose, and their struggle is a struggle for power within the Palestinian body politic.
Hundreds of families have been displaced and many buildings have been damaged amid the clashes.
At least six people were killed in two days of clashes in a Palestinian refugee camp in Lebanon.
Abbas is also hoping to persuade Hamas to join a new Palestinian unity government that would end the split between the West Bank and Gaza Strip.