At least 11 Palestinians were killed Tuesday in escalating violence in the Gaza Strip, official reports said.

Hamas militants opened fire on a National Security jeep traveling to the Karni border crossing with Israel, killing eight of Palestinian Presedent Abbas’ officers. The gunmen had been lying in an ambush near the Karni crossing, witnesses said.

It was the worst single attack since deadly clashes between Hamas and Fatah resurfaced over the weekend for the first time since the rival groups formed a unity government two months ago with the main aim of ending Palestinian infighting.

The attack near Karni came hours after members of Abbas' presidential guard shot dead a Hamas commander, Ibraheem Menia, Tuesday morning when he refused to stop at a roadblock set up by them in eastern Gaza City.

Hamas' military wing, the al-Qassam Brigades, had vowed to avenge his death.

"We will deal with Menia's murderers in the same way we deal with the Israeli occupation's spies," it said in a statement.

Two other Palestinians were killed in unrelated incident on Tuesday.