The Israeli Prime Minister said today that he was ready to give the go-ahead for a full scale military operation against Gaza to free an Israeli soldier kidnapped by Palestinian militants.

As tomorrow morning's Israeli deadline for the soldier's release approaches, Ehud Olmert ordered the army to prepare a ''prolonged and extensive military operation" against militants in the Gaza Strip, saying that he held the entire Palestinian leadership responsible for the safety of Corporal Gilad Shalit.

The 20-year-old soldier was abducted when Palestinian fighters - including members of groups linked to Hamas, the ruling Palestinian party - launched an audacious pre-dawn raid on a military post on the Israeli side of the Gaza border yesterday.

"I gave the military commanders instructions to deploy forces so that they are ready for a comprehensive and protracted operation in order to strike the terrorist organisations and their chiefs," Olmert said in a speech in Jerusalem.

"Let it be clear: We will reach everyone, no matter where they are, and they know it. There will not be immunity for anyone."

Three Palestinian groups purporting to be holding Shalit this afternoon issued a statement setting conditions for his release. The statement, signed by Hamas' military wing, the Saladdin Brigade and the Army of Islam, read: "The occupation will not get any information about its missing soldier until it commits to the following: First, the immediate release of all women in prison. Second, the immediate release of all children in prison younger than 18."

The Israeli government has given the Palestinians 48 hours to return the soldier before it launches reprisals, which could include the re-invasion of Gaza, an area it quit last year after 38 years of occupation.

Israeli tanks and heavy armoured vehicles have massed on the Gaza border ready for retaliatory operations.

Mahmoud Abbas, the Palestinian President, has condemned the attack. Saeb Erekat, a Palestinian MP close to the President, called on Israel to avoid a military response.

"We urge Prime Minister Olmert to refrain from any military action at a time when President Abbas is exerting maximum efforts in order to acquire the release of the soldier, alive and unharmed," Mr Erekat said.

The parents of 20-year-old Gilad Shalit have appealed in a letter for his safe return. "We hope that you can read these lines and we want you to know that the greatest efforts are being carried out so that you can return home," they wrote.

"We are confident that whoever is holding you also has a family, and they know what we are going through, and will know to keep you healthy and safe."

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