Two Hamas security men were killed on Tuesday evening in heavy clashes with members of the Dogmush clan in Gaza.
Palestinian sources reported 20 more men had been wounded in the exchanges of fire as Hamas lay siege to a house west of Gaza City which several clansmen have barricaded themselves in.
Hamas said in a cryptic statement that its forces came under fire while on a mission in the area. The Doghmushes said the fighting began after Hamas came to arrest a clansman and confiscate his car.
The clan, one of the largest and most powerful in the Strip, is responsible for the March kidnapping of BBC reporter Alan Johnston and involved in the kidnapping of Israeli soldier Gilad Shalit in June 2006.
Hamas officials have threatened to storm the clan's compound if the fighting continues, any such raid would likely result in numerous casualties.
Sources in Gaza have said that Hamas is determined to disarm the Dogmushes in the hopes of making an example of them to all other armed clans and groups which may threaten Hamas' rule in the region.
News agencies contributed to the report