According to a Fatah representative Hamas arrested almost 400 Fatah supporters overnight after the rally from yesterday ended in gunfire.

Fire was opened on unarmed crowds by the security forces after the rally turned into a protest against the Hamas, BBC News reports. The crowd was commemorating Arafat’s death in the Gaza City, the founder of Fatah.

Hamas claims that the Fatah gunmen opened fire and that it has only returned fire.

Seven people were killed and 130 injured in the clash.

Mahmoud Abbas, Palestinian Authority President, declared three days of mourning to “pay homage to the martyrs killed by the bullets of the putschists," referring to Hamas, ABC News reports.

The flags flew at half-mast in the West Bank, controlled by the Fatah since June.

According to the saying of a spokesman for Hamas’s Executive Force security teams, 50 Fatah members were detained on account that they are responsible for the “chaos that took place.”

On Monday almost 200,000 people participated at the rally in Gaza City turning to be the biggest rally of the Fatah since the Hamas took over last June.

Apparently the crowds of people were leaving the site after listening to speeches from Fatah leaders when the first shot was fired.

Some Fatah activists threw stones at the Hamas security forces.

Prime Minister Salam Fayyad blamed the Hamas leaders for the killings saying: “Senior officials in Hamas ordered these crimes which were carried out by the Hamas militia in order to terrify the people... Now their punishment is a national duty.”

Mr. Abbas accused “these horrible crimes committed by a band of rebels... before the eyes of the entire world,” referring to the deaths.

On Sunday Hamas broke up several Fatah demonstrations that were commemorating the third anniversary of Arafat’s death.