GAZA CITY, Gaza Strip — The U.N. chief inspected the devastation wrought by Israel's onslaught in Gaza today, leading a moment of silence at the smoldering U.N. headquarters, as the territory's militant Hamas rulers, triumphant at having survived, held victory rallies amid the ruins.

Secretary-General Ban Ki-moon, appearing stern and saddened at a ceremony at the burned out U.N. headquarters in Gaza, demanded an Israeli investigation into strikes on United Nations facilities. Ban asked the crowd to observe a moment of silence for victims of the offensive, who included nearly 40 Palestinians who had sought refuge at a U.N. school shelled by Israel.

Thousands of Hamas supporters thronged a square outside the remains of the parliament building in Gaza City, which was heavily damaged in an Israeli airstrike at the outset of the war. Two men hoisted a sign in carefully scripted Hebrew reading, "The resistance will be victorious, Israel has been defeated."

Israel and Hamas both ceased fire Sunday, after an offensive that claimed the lives of some 1,300 Palestinians, according to Gaza health officials, and 13 Israelis. The last of Israel's ground troops were expected to pull out of Gaza today if the quiet holds, defense officials said.

Israel mounted an air and ground offensive against Hamas Dec. 27 in an effort to force Gaza militants to halt their rocket fire on southern Israel and to cripple arms-smuggling operations. The fighting stopped before Israel achieved those aims.

The U.N. chief personally intervened during the war to try to stop the violence and said over the weekend he was sending a team to assess the humanitarian needs so the United Nations could issue an emergency appeal for funds.