Ban Ki-moon, the UN secretary-general, said Wednesday's declaration intended to interrupt essential services could exacerbate the Palestinians' difficult conditions.
 
"Such a step would be contrary to Israel's obligations towards the civilian population under international humanitarian and human rights law," he said on Wednesday.
 
Ban said 1.4 million people in Gaza, including the old, the very young and the sick were already suffering and "should not be punished for the unacceptable actions of militants and extremists".
 
At the same time he said continued rocket fire from Gaza into Israel was unacceptable, calling "for it to stop immediately".
 
"I understand Israel's security concerns over this matter,'' he added.
 
US backing
 
Rice assured "innocent Palestinians in Gaza"
the US would not abandon them [AFP]
Israel's move on Gaza was backed by the US on Wednesday, with Condoleezza Rice, the secretary of state, saying the Hamas was "a hostile entity to the US as well".
 
Speaking in a joint press conference with Livni in occupied Jerusalem, she said the US, however, would not "abandon the innocent Palestinians".
 
"We will not abandon the innocent Palestinians in Gaza and indeed will make every effort to deal with their humanitarian needs," she said.
 
Rice is on a visit to the Middle East in preparation for a US-led peace conference between Israelis and Palestinians.
 
The Israelis and Palestinians, however, have very different expectations of the talks.
 
Israeli leaders are seeking a softer joint declaration rather than a binding deal while the Palestinians are pushing for a firmer "framework agreement" on core issues of borders, the status of Jerusalem and refugees.
 
'Declaration of war'
 

"Under no circumstances can Israel view it as an 'enemy entity'. Gaza is not an independent state, Gaza is under occupation"

Saeb Erekat,
senior Palestinian negotiator
Tensions have been on the rise in the area since Hamas took control of the Gaza Strip in mid-June. Hamas responded to the Israeli government's announcement saying the move amounted to a "declaration of war".
 
Tzipi Livni, Israel's foreign minister, said the Israeli cabinet "made this decision according to our legal advisers, so it is according to international law".
 
But Saeb Erekat, the senior Palestinian negotiator and spokesman for the West Bank-based government, told Al Jazeera the Israeli move was "illegal and null and void".
 
"I believe Gaza and West Bank are still under Israeli occupation. Under no circumstances can Israel view it as an 'enemy entity'. Gaza is not an independent state, Gaza is under occupation," he said.
 
Erekat said Israel was in "total violation of international law" and described the move as "a collective punishment and a preparation for further military escalation against the 1.5 million people of Gaza".
 
"At the end of the day, it will not end the cycle of violence but complicate matters and breed more violence," he added.