UN chief calls for immediate Gaza ceasefire amid Israeli offensive

United Nations Secretary-General Antonio Guterres on Thursday renewed calls for an immediate ceasefire in the Gaza war.

His plea came as Palestinians started fleeing parts of Gaza City after the Israeli military began the first stages of its planned offensive there.

"I must reiterate that it is vital to reach immediately a ceasefire in Gaza, and the unconditional release of all hostages and to avoid the massive death and destruction that a military operation against Gaza City would inevitably cause," Guterres said.

Speaking in Japan where he is attending the Tokyo International Conference on African Development, he said the expanded operations would cause "massive death and destruction" in the territory.

Israel is pressing ahead with its plan to seize Gaza City despite international criticism of the operation which is likely to force many more Palestinians to move.

It already controls around 75 per cent of the Gaza Strip which has been largely destroyed and has seen the repeated displacement of large swathes of the population.

An Israeli military spokesperson on Wednesday said troops were already operating in several areas of the city to lay the groundwork for the offensive.

The official, who declined to offer a precise timetable for the operation, said the process of mobilising some 60,000 reservists would unfold over several weeks.

Prime Minister Benjamin Netanyahu has said he is "shortening the timelines" for seizing what he described as "the last terror strongholds" in Gaza.

The UN secretary-general also criticised Israel's new settlement project in the occupied West Bank which would effectively cut the territory in two.

“The decision by the Israeli authorities to expand illegal settlement construction, which would divide the West Bank must be reversed. All settlement construction is a violation of international law," he said.

The Palestinian Foreign Ministry said the construction would isolate Palestinian communities living in the area and undermine the possibility of a two-state solution

Settlement development in E1, an open tract of land east of Jerusalem, has been under consideration for more than two decades, but was frozen due pressure from previous United States administrations.

Guterres also lamented "geopolitical divides amongst superpowers" preventing the UN Security Council from stepping in to stop ongoing conflicts around the world.