Gaza has been under sustained bombardment for two days

Four Palestinian boys were killed in an Israeli attack as they played in a field in northern Gaza on Thursday.

The Israelis say their attacks are a response to the firing of Palestinian rockets into southern Israel.

A BBC correspondent says Gazan drivers are staying at home, worried their vehicles could be hit from the air.

Well into the night, Israeli air strikes could still be heard in Gaza, the BBC's Aleem Maqbool reports.

There are no signs of either the Israeli army or the Palestinian militants backing down, and the people in Israeli border towns and across the Gaza Strip are bracing themselves for more violence, he adds.

Children killed

Palestinian rocket fire killed one man in the Israeli town of Sderot on Wednesday, and has since injured others.

Israelis buried rocket attack victim Roni Yechiah on Thursday

Israeli attacks have killed Palestinian militants but also civilians including a six-month-old baby and the four boys, who doctors say had been playing football.

Israeli Prime Minister Ehud Olmert said his country could not make peace with people who were murdering its citizens.

"The only requirement we have from the Palestinians is stop killing innocent Israelis, stop shooting Qassam rockets at the civilian centres of Israel so that we'll be able to do business together," he said.

But prominent Palestinian activist Hanan Ashrawi said Israel was guilty of double standards.

"If you make security for Israel a precondition while Israel has a free hand to kill and destroy and wreak havoc in Palestinian lives, you will never get anywhere," she said.

"There has to be security for everybody."