Israeli warplanes pounded the Hamas-ruled Gaza Strip for a third consecutive day on Monday and the Jewish state prepared to launch a possible invasion after killing 307 Palestinians in the air raids.

Israel, which stepped up the air strikes after dark on Sunday, said it launched the campaign on Saturday in response to almost daily rocket and mortar fire that intensified after the Islamist Hamas group ended a six-month ceasefire a week ago.

Mark Regev, a spokesman for Israeli Prime Minister Ehud Olmert, said the military action would go on until the population in southern Israel "no longer live in terror and in fear of constant rocket barrages."

"(The operation could) take many days," said military spokesman Avi Benayahu.

Israeli tanks were deployed on Gaza''s edge, poised to enter the densely populated coastal enclave of 1.5 million Palestinians. Olmert''s cabinet approved a call-up of 6,500 reservists, a government official said.

Hamas remained defiant and the group''s spokesman Fawzi Barhoum urged Palestinian groups to use "all available means, including martyrdom operations" -- a reference to suicide bombings in Israel.

World oil prices rose up to 5.6 percent to nearly $40 a barrel on Monday as analysts said the conflict between Israel and Hamas had reminded traders of the geopolitical risk to crude supplies from the Middle East.

The U.N. Security Council called for a halt to the violence, but U.S. President George W. Bush''s administration, in its final weeks in office, has put the onus on Hamas to renew the truce.

The Israeli offensive enraged Arabs across the Middle East, where protesters burned Israeli and U.S. flags to press for a stronger response from their leaders to the attack on Gaza. Israel, whose politicians have been under pressure to act over the rocket and mortar attacks ahead of a February 10 election, was feeling little international pressure to halt its offensive, said an Israeli official, who declined to be named.