The top United Nations humanitarian official arrived in Jerusalem on Wednesday to begin an assessment of the needs on the ground in the Gaza Strip following the three-week Israeli military offensive that came to a halt just a few days ago, UN officials announced.

UN Under-Secretary-General for Humanitarian Affairs John Holmes will lead a humanitarian needs assessment team into Gaza on Thursday, together with the UN special coordinator for the Middle East peace process, Robert Serry, the officials said.

During his four-day mission, Holmes is scheduled to meet with UN staff in Jerusalem and Gaza, as well as representatives of aid agencies, civil society and donors.

Holmes "plans to stress the need to facilitate quick delivery of humanitarian aid to Gaza," the UN Office for the Coordination of Humanitarian Affairs (OCHA) said in a news release.

The 22-day offensive, which Israel launched on December 27 with the stated aim of ending Hamas rocket attacks, claimed more than 1,300lives, 412 of them children, and wounded more than 5,450, 1,855 of them children, as well as causing widespread destruction and suffering. The United Nations is the only international player remaining in the war-ravaged Gaza after Israel launched air strikes on the territory.

The bombing and shelling caused extensive damage to civilian facilities throughout the Gaza Strip, and supplies of basic food and fuel, and the provision of electricity, water and sanitation services remain critical.

Holmes, who is also UN emergency relief coordinator, will examine the damage wrought to buildings and infrastructure, including UN properties, by the violence, the officials said. He is also expected to visit the facilities of the UN Relief and Works Agency for Palestine Refugees in the Near East (UNRWA), where tens of thousands of Palestinian civilians sought shelter after fleeing their homes during the military operation.

UN Secretary-General Ban Ki-moon had announced he would dispatch an assessment team after Israel declared its unilateral cessation of hostilities on Saturday. Ban was able to see the devastation first-hand when he visited Gaza on Monday, the culmination of a diplomatic mission that took him to several capitals in the region.

"This is shocking and alarming. These are heartbreaking scenes. I am deeply grieved by what I have seen today," the secretary-general said as he surveyed the aftermath.

Meanwhile, OCHA reported Wednesday that Gazans displaced during the military operation continue to make their way home, but many of them are now homeless due to the extensive destruction of homes. As a result, they remain with host families or in UNRWA-run shelters. There were more than 18,000 people remaining in 30 shelters as of Tuesday.

OCHA also reported that the Gaza crossings at Erez, Karni, Nahal Oz, Kerem Shalom and Rafah were all open on Wednesday. However, the majority of mills and bakeries in Gaza remain closed due to a shortage of wheat flour and cooking gas, resulting in an acute shortage of bread.

The World Food Program (WFP) is trying to help by delivering flour to bakeries, and WFP-contracted bakeries are now working to produce 5,000 three-kilogram bread parcels per day. WFP also reports that a first shipment of 10 tons of nutritious date bars --supplied by Egypt under WFP's Operation Lifeline Gaza -- made it into Gaza Tuesday.

At the same time, the UN agency remains concerned by security constraints, which are limiting access to its warehouses. It does not have access currently to some 520 tons of food, or 12 percent of WFP's current stocks in Gaza.

Meanwhile, a vaccine storage facility in Gaza is now functional, and routine vaccines will be available until March, thanks to support from the UN Children's Fund (UNICEF). In addition, two UNICEF-supported therapeutic centers are working at full capacity to provide services for 120 malnourished children per day, the officials said.

UNICEF also managed to deliver six trucks of family hygiene kits to needy Gazans Tuesday, and get more than 1,300 water purification tablets into Gaza --enough to purify drinking water for 30,000 people for the next three months.

In an attempt to get schools up and running again as soon as possible, UNICEF is working to repair windows, desks and chairs at schools, as well as to provide clean sanitation facilities for girls. It is also providing a first wave of 40,000 students with school supplies.

OCHA added that only US$63 million of the US$117 million needed for priority projects in Gaza has been committed or pledged so far.