Tel Aviv/Gaza  - A unilateral ceasefire declared by Israel in the Gaza Strip was "fragile" and Israel would respond "without hesitation" if its troops in the salient were attacked, Prime Minister Ehud Olmert said Sunday morning.

The premier made the comments at the weekly cabinet meeting, following attacks on Israeli forces, and rockets from the Strip at southern Israel, hours after the ceasefire went into effect at 00:00 GMT Sunday (2 am local time.)

"We have operational freedom to respond if terror organizations continue attacks," media reports quoted Olmert as saying.

Despite Olmert's ceasefire announcement, militant Palestinians in the Gaza Strip launched rockets and mortars into the Israeli border area near the town of Sderot Sunday, damaging a chicken coop, but causing no injuries, a military spokeswoman said.

Israeli troops also came under fire by a group of Palestinians in the northern Gaza Strip, the Israeli army said. The troops informed Israeli armoured units and air force which then shot at and hit the Palestinians, said the spokeswoman.

Announcing the ceasefire, Olmert told a news conference Saturday that Israel had achieved the aims it set for itself when launching its Operation Cast Lead against Hamas in the Gaza Strip on December 27, and was therefore calling a halt to the fighting.

He also apologised for the heavy Palestinian casualties caused by the incessant Israeli attacks, but said Israeli troops would, for the time being, remain in the Gaza Strip, which they entered on January 3, and would respond if attacked.

Hamas rejected Israel's ceasefire announcement, and in fact greeted it by launching a rocket salvo at the city of Beersheba.

A statement issued by the Islamist group on Sunday morning congratulated the Palestinians on "a great victory" and said it "had caused heavy losses to the enemy and forced it to withdraw."

Palestinian medical officials report that at least 1,203 Palestinians were been killed and over 5,100 injured since Israel began its military campaign on December 27.

Three Israeli civilians and 10 soldiers were killed.

Israel was also going to set up a forward emergency room at the Erez crossing on the Gaza-Israel border, to treat Palestinian wounded, the Israel foreign ministry said Sunday morning.

Egyptian President Hosny Mubarak, who tried to mediate an end to the Gaza fighting, was expected meanwhile to host a conference on the crisis on Sunday.

Jordan's King Abdullah II, British Prime Minister Gordon Brown, French President Nicolas Sarkozy, German Chancellor Angela Merkel, UN Secretary-General Ban Ki-moon, are expected to attend the summit in the Egyptian Red Sea resort of Sharm al-Sheikh.

Israel launched its Operation Cast Lead against Hamas in the Gaza Strip three weeks ago, following sustained rocket fire from the salient on southern Israeli towns and villages. dpa