GAZA CITY, Gaza Strip – Rival Palestinian gunmen exchanged fire at two Gaza hospitals on Monday and Cabinet ministers fled their weekly meeting after the government headquarters was caught in the crossfire in the latest round in an increasingly brutal power struggle between Hamas and Fatah.

In all, 12 Palestinians were killed Monday, including three shot dead in Beit Hanoun Hospital in northern Gaza. Combatants fired mortars, grenades and assault rifles at Gaza’s largest hospital, Shifa.

After sundown Monday, gunmen, apparently from Hamas, laid siege to the house of Jamal Abu al-Jediyan, the senior Fatah official in northern Gaza. They then dragged him outside and killed him, security officials said. Medics said he was hit by 45 bullets.

Al-Jediyan was a top aide to Gaza Fatah strongman Mohammed Dahlan. Al-Jediyan’s brother was also killed, apparently in the same shoot out.

Fatah spokesman Maher Mikdad harshly denounced the killing and pledged revenge.

“What is this, if not a war,” he said.

Fatah called on its members to target all Hamas political and military leaders.

The battles came a day after two militants from the rival sides were dragged onto high-rise rooftops and thrown to their death in a conflict that appears to be rapidly descending into all-out confrontation. Early Monday morning, shots were fired at Prime Minister Ismail Haniyeh’s home.

Appeals for calm by the leaders of the two rival camps, President Mahmoud Abbas of Fatah and Haniyeh of Hamas, went unheeded. Repeated attempts to secure a cease-fire have failed.

Monday’s deaths brought to 78 the number of Palestinians killed since the latest round of infighting erupted in May. “I call on everyone to stop this immediately, not only because of the examinations, but also for our people to live a normal life,” said Abbas.