Yesterday, Hamas police broke into the house of Dr. Abdullah Abu Samhadana, a Fatah minister in Gaza, and left an arrest warrant (he wasn't home.) This was only the most recent of a series of arrests by Hamas in Gaza, which are usually mirrored by arrests of Hamas members in the West Bank by the PA.
This time, however, the Al Aqsa Martyr's Brigades released a statement threatening Hamas for these arrests, saying "Silence is no longer possible for the actions of Hamas against the sons of Fatah in Gaza, the latest being the storming of the house of fighter Abdullah Abu Samhadana. We in the Al Aqsa Martyrs Brigades announce clearly that our silence is running thin."
The only problem is that the Al Aqsa Martyr's Brigades in Gaza has been decimated by Hamas, so it is probably an empty threat.