The Gaza conflict raged on yesterday after both sides dismissed a UN call for an immediate ceasefire, and Israel indicated it may move its forces deeper into densely populated urban areas.

A meeting of Israel's security cabinet rejected a ceasefire resolution passed by the Security Council in New York while air and ground attacks continued in Gaza, killing 22 more Palestinians and raising the death toll to at least 800, according to the head of Gaza emergency services. Hamas fired a fresh barrage of rockets across the border, hitting the cities of Beersheba and Ashkelon. Thirteen Israelis have died since the Gaza offensive was launched on 27 December.

The office of Israeli Prime Minister Ehud Olmert said rocket attacks demonstrated the futility of calling for an immediate ceasefire. A statement said it "only proves that the UN's decision is unworkable and will not be adhered to by the Palestinian murder organisations". A spokesman for Hamas said they were "not interested" in a ceasefire because they had not been consulted over the draft resolution which failed to meet their minimum demands.

The Israeli government said the draft did not provide adequate measures to stop weapons being smuggled in and Hamas said it did not address the issue of tunnels to the Egyptian border, Gaza's lifeline to the outside world, being blocked by the Israelis and it did not accept the presence of Israeli forces in Palestinian territory. Hamas accused the US, which abstained from voting, of weakening the resolution to buy Israel more time.

The Israeli government is said to be studying high-risk plans to send troops into the heart of Gaza City to destroy Hamas's military capabilities, which is likely to lead to heavy civilian casualties as well as Israeli losses.

Relations between the Israeli government and the UN and other international bodies continued to deteriorate with starkly contradictory accounts of two incidents involving the deaths of civilians. Food deliveries to Gaza were suspended on Thursday after the UN and the Red Cross accused the Israelis of firing on a relief convoy. And yesterday, the UN high commissioner for human rights, Navi Pillay, called for an independent investigation into reports that Israeli forces herded Palestinians into a house in Gaza and opened fire on the building the next day, killing 30. Ms Pillay said the killings "appear to have all the elements of war crimes ... It cries out for proper investigation". The Israeli military said their investigation showed both claims were false.

The UN's food relief agency, the World Food Programme, said that it was becoming increasingly difficult to find food in Gaza, with many people too frightened to leave their homes, and supplies scarce and dwindling.