By Bassam Masoud and Nidal al-Mughrabi GAZA/CAIRO (Reuters) -Israel ordered residents out of the centre of Gaza’s main southern city Khan Younis on Saturday and pounded the length of the enclave, after the United States wielded its U.N. Security Council veto to shield its ally from a demand for a ceasefire. Since a truce collapsed last week, Israel has expanded its ground campaign into the southern half of the Gaza Strip by pushing into Khan Younis. Simultaneously, both sides have reported a surge in fighting in the north. Israel’s Arabic-language spokesperson posted a map on X highlighting si…