Two people were killed and one arested when Hamas security forces attacked a house in Gaza on Tuesday.
They were suspected of involvement in the murder of an Italian citizen.
Vittorio Arrigoni, 36, a pro-Palestinian activist, was abducted last Thursday and hanged.
His body was found in an abandoned house in the north of the Gaza Strip.
The BBC reports the killing was widely seen as a challenge to the authority of Hamas.
It was the first kidnapping of a foreigner since Hamas came to power in 2007.