Unidentified persons set off bombs at two Hamas security compounds in the Gaza Strip on Sunday, causing no casualties, the Palestinian Islamist group said.
There were no immediate claims of responsibility for the attacks on the Ansar-2 prison and the Gaza residence of Palestinian President Mahmoud Abbas, whose secular Fatah faction was forced out of the territory by Hamas in a 2007 civil war.
Security sources in Israel, which fought a December-January war with Hamas, denied involvement. Internal and sometimes violent challengers to Hamas's rule include surviving Fatah cells and breakaway Islamists professing allegiance to al Qaeda.
A Hamas security official said that the explosions, which took places within minutes of each other and which local residents described as sounding consistent with hand-laid bombs or grenades, had hurt no one.
"An investigation is under way," the official said.
With Abbas now based in the West Bank, his Gaza residence is under Hamas control and some Fatah members say they were detained there. Hamas has not confirmed that the building is used as a stockade.