UN humanitarian chief John Holmes appealed to Israel to re-open border crossings into the besieged Gaza Strip to allow delivery of badly needed relief aid in the wake of the devastating 22-day conflict.

"Israel has a particular responsibility as the occupying power in this context, because of its control of Gaza''s borders with Israel, to respect the relevant provisions of international humanitarian law," Holmes told the 15-member UN Security Council during a briefing on his recent visit to the region.

"It is therefore critical that new steps are taken immediately by the Israeli authorities to move to the sustained re-opening of crossing points," he said.

He underscored the importance of improving the living conditions of Gaza''s 1.5 million people to avoid further despair and undermining efforts to find a lasting solution to the Israeli-Palestinian conflict.

More than 1,300 Palestinians were killed and another 5,300 wounded in Israel''s land, sea and air assault on Gaza, which was launched on December 27 to stop Hamas firing rockets at southern Israel and ended January 18.

On the Israeli side, three civilians and 10 soldiers were killed in combat and by rocket fire.

"Everybody stressed the urgency of reopening the crossing points," France''s UN Ambassador Jean-Maurice Ripert, who chairs the council this month, concurred.

Speaking to reporters after the briefing, Holmes also said the world body planned to launch a flash appeal next Monday for "several hundred million dollars" to assist the beleaguered Gaza population.

"We can''t really perform that operation fully, none of the (UN) agencies will be able to do that, unless the crossing points are open on a sustained basis not only for humanitarian goods but also for staff and also for commercial goods, and for example cash to enable the economy to flourish," he added.