Israel eased a blockade of the Gaza Strip on Friday but militants there aimed rockets and mortars across the border, one of which misfired and killed two Palestinian girls.

Israel said it was responding to numerous requests from the international community by reopening border crossings with Gaza to allow in vital truckloads of fuel and humanitarian aid.

But renewed fire from Gaza-based militants - a day after Israeli Prime Minister Ehud Olmert warned Islamist group Hamas to stop firing rockets or pay a heavy price - ensured that the easing of tension was short-lived.

About a dozen rockets and mortar bombs were fired from Gaza on Friday. One accidentally struck a northern Gaza house killing two Palestinian sisters, aged five and 13, and wounding a third, Palestinian medics said.

No militant group claimed responsibility. Hamas police said they would investigate.

An Israeli military spokesman said the Erez border crossing, the main passage for people between Israel and Gaza, was closed after two mortar bombs fell in that area.

The earlier reopening was seen as potentially easing tensions that might have led to military action to end rocket attacks, though in the past Israel has allowed Gaza to resupply with vital goods before launching assaults.

Palestinian workers at the crossings said fuel had arrived for Gaza's main power plant, where shortages mean periodic blackouts for many of the territory's 1.5 million residents.

Raed Fattouh, coordinator of supplies, said about 100 trucks loaded with grain, humanitarian aid and goods for the private sector were due to come in to Gaza during the day, including a convoy from Egypt.

Israel also let a Palestinian man go to an Israeli hospital for treatment for an injury after a militant rocket struck his home in Gaza earlier this week, medics and officials said.

Gaza, a largely impoverished coastal enclave, has been under a heightened Israeli blockade since Hamas seized control of the territory from Western-backed Palestinian President Mahmoud Abbas's Fatah movement in 2007.

In renewed fighting since a six-month truce expired last week, at least six militants have been killed by Israeli air strikes and dozens of rockets and mortar shells from Gaza have slammed into Israel, damaging homes and causing panic.

Israel's cabinet plans on Sunday to debate a decision by a security panel to hit back at Gaza militants, beginning with air strikes on Hamas targets, political sources said.

Israel withdrew its forces and settlers from Gaza in 2005 and Olmert has said he does not wish to re-occupy the coastal strip. A military offensive could involve ground combat likely to result in high casualties.

Israeli Foreign Minister Tzipi Livni discussed the crisis on Thursday with President Hosni Mubarak of Egypt, which borders Gaza to the west and which brokered the truce in June. Mubarak urged restraint on both sides.

At the same time, Olmert appeared on an Arabic television channel, urging Gazans to reject their Islamist rulers and stop the rocket attacks.

He said it was a last-minute appeal and said he would not hesitate to use Israel's military might if they did not.-Reuters