Israel's supreme court ordered the government last night to justify its stranglehold on the Gaza Strip amid concern that Palestinian civilians will face dire humanitarian consequences due to punitive energy cuts.

The intervention came as the administration of Ehud Olmert, the prime minister, was accused by the European Union of inflicting "collective punishment" on the territory's civilian population by cutting fuel and electricity supplies.

Menahem Mazouz, the state prosecutor, said: "Security chiefs must carry out supplementary examinations to take account of the humanitarian obligations before ordering electricity cuts."

Israel has been steadily tightening the noose on Gaza in an effort to put pressure on the territory's Hamas rulers to stop the daily rocket barrages.

On Sunday the Palestinian fuel authority reported that petrol and diesel deliveries were down by more than 40 per cent.

Residents of Gaza City lined up at petrol stations to fill their cars in anticipation of looming shortages. With Israeli electricity and fuel accounting for 91 per cent of Gaza's power output, the latest cuts could have severe humanitarian consequences.

The court's action came after 10 Israeli and Palestinian human rights groups asked it to issue an injunction against the punitive cutbacks, which they argued amounted to collective punishment of 1.5 million Gazans in a practice banned by international law.

In an affidavit to the court, Gaza's water authority said that dwindling fuel and electrical supplies could jeopardise sewage treatment and residents' access to clean drinking water.

The court gave the state five days to respond to the groups' petition before ruling — a delay that frustrated rights activists but still represented a blow to Mr Olmert's policy.

Benita Ferrero-Waldner, the EU's commissioner for external relations, who is visiting Jerusalem, said: "I think collective punishment is never a solution."

Israel has given warning in recent weeks that a broad offensive against Gaza may be inevitable if the rocket fire continues.

The energy cuts are only the latest blow to Gaza which is reeling under an Israeli siege that has grown more punishing with each passing week. Virtually all non-essential items have been kept from entering the Gaza Strip.

Fresh fruit, meat, cooking oil, cigarettes and beverages are all in dwindling supply. Prices have shot up. Medical supplies are also running low, according to the World Health Organization.

Israel has also restricted fishing to within six miles of shore.

As a result, this year's lucrative sardine catch is down 60 per cent from last year.

Defending the policy yesterday, Binyain Ben-Eliezer, the Israeli infrastructure minister, said: "What's the alternative? The alternative is that tomorrow or the next day we'll be forced to bring three or four divisions and go into Gaza. What will the results be then?"