The witnesses said an Israeli army undercover unit stormed the Jamal Abd al-Nasr neighbourhood of Tulkarim and assassinated six alleged members of al-Aqsa Brigades, the armed wing of Arafat's Fatah movement.
The soldiers entered the area disguised as Palestinians, witnesses said. Medics said the undercover unit was assisted by uniformed soldiers, who surrounded the house in which the six were staying.
Among the dead were Hani Uwaida, the alleged al-Aqsa Brigades commander in the northern West Bank area. Ambulances were seen carrying bodies and the injured from the area.
The Israeli occupation army confirmed the killings, saying they died in a shootout with Israeli border guards.
Missiles destroy home
In a separate incident an Israeli F-16 fighter jet fired two missiles that destroyed an apartment block in Gaza City's Zaitun neighbourhood after dark on Sunday, Palestinian security sources said.
A four-year-old boy was also wounded when he fell down the steps of a neighbouring house due to the force of the blast, medics said.
The Israeli army had no comment on the raid.
The same building was attacked earlier in the day with rockets by an Israeli helicopter gunship, injuring four bystanders.
Witnesses said it was the home of a Hamas member.
Elsewhere in Gaza, seven Palestinians were wounded when Israeli soldiers opened fire on Khan Yunis after a rocket attack on an Israeli settlement, medics said.