ISRAEL and Hamas have both threatened to escalate attacks on each other amid Israeli preparations for a protracted air and land strike on Gaza.

As the stand-off between Israeli troops and Palestinian militants entered its second week, the UN special envoy to the Middle East rebuked Israel for destroying civilian buildings in Gaza and urged it to abide by international law.

Days after Israeli jets crippled Gaza’s only power station, Álvaro de Soto inspected the still-smoking ruins to hear that the plant would be shut for at least six months, leaving hundreds of thousands of Palestinians without power.

Israel yesterday restarted fuel supplies and partially reopened the Karni cargo crossing for food and medical supplies into Gaza, after warnings of a humanitarian crisis. But its artillery batteries and warplanes continued to strike the otherwise sealed-off coastal strip, with helicopter gunships firing missiles into the office of Ismail Haniya, the Palestinian Prime Minister.

Ehud Olmert, the Israeli Prime Minister, is losing patience with attempts to free Corporal Gilad Shalit, who was captured by the Islamists’ armed wing eight days ago. He told his Cabinet that he had instructed the military “to do everything in order to bring Gilad back home . . . and when I say everything, I mean everything”.

Mr Olmert had put a large-scale military offensive on hold to give Egyptian-led negotiations a chance. Hamas’s armed wing, the Izz al-Din al-Qassam Brigades, threatened yesterday to answer Israel’s “dirty war” — the destruction of the power plant, university buildings and the Interior Ministry — with its own strikes on civilian targets.

“If its operations continue, we will hit the occupation targets we were previously reluctant to strike,” Abu Ubaida, a Hamas military spokesman, said. Continued Israeli attacks would, he said, plunge the region into a sea of blood.

Señor de Soto called on Corporal Shalit’s kidnappers to release him as soon as possible, saying: “It does not serve any Palestinian interest to continue to hold this hostage.” However, he said that the UN was “very alarmed at the situation, particularly the humanitarian one”. He reminded Israel of its obligations under international law not to punish civilians and to ensure that it did not react with undue harshness.

“We are fervently hoping that Israel will show restraint and observe international law and particularly the rules regarding proportionality,” Señor de Soto said after visiting Mahmoud Abbas, the Palestinian President, in Gaza City.

“For instance, we find it difficult to understand that the power plant was struck and certain other measures taken as well. There have been several actions of this nature, including the arrest, the detention of ministers and legislators.”

Both Señor de Soto and Mr Abbas visited Gaza’s stricken power station. They were told by engineers that it would take six to eight months to get the 140 megawatt plant working again. The strike will leave Gazans suffering lengthy power cuts and entirely dependent on electricity from Israel.

Señor de Soto said that any long-term political solution would need functioning Palestinian ministries and infrastructure. He said: “If you are going to have a two-state solution, you need a viable Palestinian state.”

Mr Olmert told his Cabinet that Israel “has no interest in harming the Palestinian population”, but said: “We are responsible for the peace of the state of Israel and its citizens. It is out of this responsibility that we will strike at anyone who tries to hurt us. Nobody will be exempt.”

Israeli newspapers have reported that Yuval Diskin, the country’s internal security chief, told the Cabinet that the Shalit crisis might be prolonged. “We have to take a deep breath,” he said. “This could take weeks or months. There is no magic solution.”

Nabil Abu Rudeineh, Mr Abbas’s spokesman, said that the negotiation efforts were continuing but “near a dead end”.

Last night the Israeli Army said it had killed three Palestinian gunmen during a confrontation at Gaza’s disused airport.

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