Supplies for generators at Al-Shifa hospital are said to be very low

The army said one was about to launch mortar shells at Israel from near Gaza City - a claim disputed by Hamas. Three died in fighting near the Gaza border.

Israeli troops have killed about 20 people in the coastal strip in less than a week, mostly Hamas members.

The incidents come as medical officials in Gaza say hospitals are beginning to run out of vital fuel supplies.

Israel says its actions in Gaza are a response to security threats, including the regular firing of rockets into its territory.

'Collective punishment'

The BBC's correspondent in the Palestinian territories, Aleem Maqbool, says it is not just military pressure that Israel is exerting on Gaza. Sanctions have been imposed as well.

These include the reduction of fuel supplies upon which Gaza depends. On Sunday, the Fuel Companies Association there said it refused a delivery after it was offered just one-quarter of the normal amount it receives.

The association's chairman said accepting such low supplies would amount to participating in what he called "collective punishment by Israel".

Officials say most petrol stations in Gaza have shut, and that medical patients are now at risk because fuel supplies at hospitals - vital for running generators - are running out.

There has been good news for some, our correspondent says: Israel allowed around 250 people to leave Gaza for Egypt.

Most either study or work abroad, but had been trapped since June, following the Hamas takeover of the territory, when Israel imposed strict travel restrictions.

Several thousand people, needing to get out of Gaza, have registered with the Israeli authorities.

They include medical patients, some of whom have died in recent weeks, waiting for treatment only available outside Gaza.