UN Secretary-General Ban Ki-moon, voicing shock and anger at the "heartbreaking" devastation, visited the Gaza Strip on Tuesday to pledge aid for Palestinians after Israeli attacks killed 1,300 and made thousands homeless. "I have seen only a fraction of the destruction. This is shocking and alarming," Ban said, condemning an "excessive use" of force by Israel as well as Hamas's rocket fire into Israel. "These are heartbreaking scenes I have seen and I am deeply grieved by what I have seen today," he told a news conference held against a backdrop of still smoldering food aid in a UN warehouse set ablaze by Israeli gunfire last Thursday. Ban called the attack "outrageous" and demanded an inquiry and, if need be, the guilty to be held to account. Israel blames Hamas for fighting around civilians and sites run by the United Nations, which provides support for much of the 1.5 million population. Most are from families of refugees who fled or were forced from homes in what became Israel in 1948. Ban, on a Middle East tour, was the most senior diplomatic figure to visit the territory in years, certainly since Hamas routed secular Fatah forces loyal to Western-backed Palestinian President Mahmoud Abbas and seized control of Gaza in June 2007. "I appeal to Fatah, Hamas, to all Palestinian factions, to reunite within the framework of the legitimate Palestinian Authority," Ban said, urging an end to a schism between Hamas in Gaza and Abbas in the West Bank that has paralyzed peace talks. Thousands of Hamas supporters, many waving green Islamist banners, marched through Gaza and held a rally outside the compound during Ban's visit. Speakers demanded U.N. recognition. "The Hamas government was elected by popular vote," one said. "We demand an end to double standards." The United Nations, with other key mediators in the Middle East, say they will only deal with Hamas if it recognizes Israel, renounces violence and accepts interim peace deals. Israeli leaders hope the devastation wrought on Gaza will undermine Hamas's popularity. There is some sign of impatience. Watching the rally outside buildings marked by the latest war, Wael Eid said: "Hamas overestimated its own strength ... and brought this greater destruction. "We've been let down by everyone in the world, so now we should seek a peace settlement with Israel." An Israeli security source said much of the pullout was completed as planned, before Obama's inauguration, though some forces remained inside the enclave. Analysts saw the withdrawal as an effort to avoid any tension with the new president. Many Palestinians returned to the rubble of what used to be their homes in Gaza city suburbs that were hard hit during the fighting. They picked through debris, salvaging belongings. "We've won the war, but we've lost everything," said Nabil Sultan, commenting on Hamas's "V for Victory" signs as he surveyed the rubble of his home on the city outskirts. "This was my house," he shrugged, beside a pile of smashed concrete. Two children were killed by bombs left behind in Gaza, Hamas officials said. There were scattered and contradictory reports of occasional firing but no clear breach of the ceasefire. Ban, who met Israeli Prime Minister Ehud Olmert before traveling to Gaza, later visited southern Israel, an area hit by Palestinian rocket fire for years. At Olmert's office, Ban said he wanted to help to make the ceasefire "durable." Gaza medical officials said the Palestinian dead included at least 700 civilians. Israel says hundreds of militants died. The United Nations has estimated some $330 million is needed for urgent aid. Reconstruction, if it can be launched in light of the frost between Hamas and the West, may cost close to $2 billion, according to Palestinian and international estimates. The U.N.'s nuclear watchdog said on Tuesday it would look into a claim by Vienna-based Arab ambassadors that Israel may have used ammunition containing depleted uranium in Gaza attacks. Israel said it hoped to more than triple the number of trucks delivering supplies to about 500 a day.