Hospitals in the southern Gaza Strip have only three days of fuel left due to closed border crossings, the head of the World Health Organization said Wednesday. Despite international objections, Israel sent tanks into the overcrowded southern city of Rafah on Tuesday and seized the nearby crossing into Egypt that is the main conduit for aid into the besieged Palestinian territory. WHO director-general Tedros Adhanom Ghebreyesus said fuel that the UN health agency had expected to be allowed in on Wednesday had been blocked. The Israeli authorities control the flow of humanitarian aid into Gaza….