Doctors Without Borders says thousands of people are unable to evacuate from Nasser Hospital in Khan Younis — one of two remaining hospitals in southern Gaza able to treat critically wounded patients — because of the danger of the surrounding area, despite an Israeli order to leave. Fighting has intensified in the city in recent days, and Israel says its troops have encircled it. Israel is trying to create a buffer zone on the Gazan side of the enclave’s border with Israel, Israel Defense Forces spokesman Daniel Hagari said Tuesday, after 21 Israeli soldiers were killed while placing mines as part of the effort.