Tel Aviv - Israel gave Hamas and other Palestinian militant factions in Gaza 48 hours Friday to avoid an Israeli military operation in the strip, government officials said.

For the first time in 10 days, it opened its border crossings with the Gaza Strip Friday morning to allow in essential humanitarian supplies.

If Hamas, the radical Islamist movement ruling Gaza, responded by reducing rocket and mortar attacks from the strip, Israel would put off a military operation that would seek to end the attack, the officials said.

A final decision on an Israeli military response against the surge in rocket and mortar attacks from Gaza - which followed the formal end of a six-month truce one week ago - will be taken in a meeting of caretaker Prime Minister Ehud Olmert's inner security cabinet Sunday.

"We are bringing in humanitarian aide before we enter with troops into the Gaza Strip," one official, who spoke on condition of anonymity, told the Ma'ariv daily Friday.

"In other words, if in the course of the weekend Hamas takes one step back and stops the fire on the Gaza periphery communities, Israel will not rush into a harsh retaliation."

The government official said Israeli Defence Minister Ehud Barak "has still not given up the option of averting a large military force entering into Gaza, but if Hamas continues its fire, we will have no other choice but to respond decisively."

Some 40 trucks with basic food products and medical supplies, donated among others by Egypt and the United Nations, passed through the Kerem Shalom crossing with southern Gaza Friday morning, while another 40 trucks with grain, mainly wheat, also passed through the Karni crossing for commercial goods, east of Gaza City, an Israeli defence official said.

A limited supply of industrial diesel for Gaza's only power plant as well as cooking gas also entered through the Nahal Oz fuel crossing, said Major Peter Lerner of the Defence Ministry's office which coordinates Israeli government activities in Gaza and the West Bank.

He said the aid shipment was the first since December 16.

A shipment scheduled to enter on Wednesday had been cancelled at the last minute following massive rocket and mortar fire the previous days.

The attacks, meanwhile, continued also Friday, with Palestinian militants launching at least seven mortar shells at southern Israel overnight, a military spokesman in Tel Aviv confirmed, although Israeli media reported a larger number - as many as 20.

Most fell in open fields in the southern Israeli Eshkol region, but one struck inside a community and damaged an empty building. (dpa)