TEL AVIV — A humanitarian crisis is unfolding in Gaza after Israel ordered a “full siege” of the territory, causing shortages of electricity, food and water in retribution for Hamas’s deadly attack on Israel. The Palestinian Health Ministry in Gaza said health services have reached a “critical stage,” with medicine and fuel expected to run out “imminently” and hospitals at full capacity. U.S. Secretary of State Antony Blinken arrived in Israel on Thursday and will focus on lending support for Israel while handling the issue of unaccounted-for Americans either killed, in hiding or taken hostage by Hamas. In recent days, Israel has massed troops near Gaza and called up a record number of 360,000 reservists ahead of an expected ground assault, as Israel Defense Forces continue to target senior Hamas leaders and infrastructure.