BETHLEHEM, West Bank, 18 July — Israel killed four Palestinians in an air raid on Bethlehem yesterday that destroyed a house packed with women and children and raised talk that their bitter conflict was moving a step closer to war.

Late at night, the Israeli Army deployed military reinforcements in the West Bank. Troops and tanks were sent to various parts of the West Bank including around Bethlehem. “At this time the Israeli Army is mobilizing infantry and armored vehicles” to the West Bank,” military officials said.

The mid-afternoon helicopter assault killed at least two activists of the Hamas movement and wounded 14 people, including a young girl who lost her arm, hospital sources said.

“The Palestinian National Authority strongly condemns this gross aggression and considers it an act of war perpetrated by the Israeli government against the unarmed and innocent Palestinian population,” a Palestinian statement said. “From now on the cease-fire has no meaning,” the main umbrella group of Palestinian movements warned after the raid. Forty-five-year-old Omar Saada, a local official of Hamas was among the four killed.

Witnesses said another Hamas member, 40-year-old Taher Al-Arouj, was also killed along with two more members of the Saada family, who reportedly had gathered to welcome a relative returning from an Israeli jail.“The whole family was waiting in the garden,” one family member told AFP, adding that nearly 40 people were on the scene at the time. “This was a massacre.”

Palestinian police arrested five suspected collaborators in Bethlehem accused of helping the Israelis carry out the day’s deadly raid, security sources said.

Prime Minister Ariel Sharon’s office said he had called US President George W. Bush and warned that Israel would defend itself in the face of the ongoing violence, which has continued despite the US-brokered cease-fire.

The Palestinians say Israel has assassinated around 40 activists since the Palestinian uprising was launched in late September. More than 650 people have been killed since then.

The National and Islamic Forces, a coalition of Palestinian groups, said in a statement that all Israeli settlers and soldiers would now be considered targets after the raid on the Saada house.

A mortar bomb was fired on Jerusalem later yesterday, in what the army said was the first such attack since the eruption of the intifada, triggering a retaliatory helicopter raid on a nearby West Bank village.