RAMALLAH, June 24: Israeli forces stepped up their campaign against Palestinians on Monday, retaking Yasser Arafat’s home base of Ramallah and killing six people in a helicopter raid on the Gaza Strip.

Israeli Prime Minister Ariel Sharon warned that the Gaza raid was only a taste of things to come and the army was preparing a “massive military operation” against Hamas in the territory.

Israeli troops, backed by dozens of tanks as well as helicopter gunships, moved into Ramallah for the third time this month, imposing a curfew and sealing off Arafat’s already-battered compound.

At the same time, helicopter-fired missiles killed six Palestinians, including two military officials of Hamas, riding in two cars on the southern Gaza Strip. Palestinian officials said they were “targeted killings”.

Two senior Hamas members, Yasser Rizk, 29, and Amir Koffa, 28, were among those killed, a Hamas official said.

The Israeli army acknowledged killing Rizk, saying he was behind a Jan 9 attack that left four soldiers dead and was also organizing new suicide bombings in Israel.

The helicopter attack drew threats of reprisals from Hamas, which claimed responsibility for the June 18 suicide bombing of a bus that killed 19 Israelis as well as the bomber.

Palestinian security officials, often criticized for not doing enough to stop suicide bombings, also put Hamas’s spiritual leader, Sheikh Ahmed Yassin, under house arrest in Gaza City.

RAMALLAH AGAIN: Palestinian security sources said between 50 and 60 tanks, armoured personnel carriers and other vehicles rolled into Ramallah before dawn, with at least two helicopter gunships in support.